WO2012038244A1 - Injection molded micro-cantilever and membrane sensor devices and process for their fabrication - Google Patents

Abstract

The microdevice according to the present invention is an element which comprises a body element of a few mm size and a thin membrane or cantilever like element which gains additional functionality by incorporating a micro- or nanopattern (either topography or chemical modification) on one side of the cantilever or membrane like part. The device is fabricated by micro-injection molding with a microfabricated or micromachined mold cavity. By using an additional foil-like mold, functionality is added to the microdevice without major modifications of its shape, outlines and volume. Thus mechanical and optical properties can be modified, simply by adding an additional device/element (an optical diffraction grating), a roughness (for controlling biocell adhesion and growth) and selectivity (for selection by size, shape). Also mechanical performance (stiffness, resonance frequency) can be modified by corrugations in the thin areas of the cantilevers or membranes. Due to the flexibility of the process, modifications of the setup can be done easily with little effort, i.e. without fabricating a new mold. The invention is based on the method for surface patterning of foils.

Description

Injection molded micro-cantilever and membrane sensor devices and process for their fabrication

The present invention relates to an injection molded micro- cantilever and membrane sensor devices and process for their fabrication .

A cantilever is typically an extended beam with an aspect ratio (length to thickness) in the range of 2 to 1000, which is fixed at the body at one side and free to oscillate at the other side. A membrane is fixed at least on two sides and is able to oscillate between these fixations. Most common are membranes which are fixed into a frame, like a diaphragm for pressure sensing.

The manufacturing of microcantilevers using injection molding is known in the art having a symmetric set-up having the advantage that during demolding the device experimences minimum stress (US2004/0208788A1 ) . It is disadvantageous that the surface of the cantilever is barely accessible for

additional structuring. More advantageous is the manufacturing of similar shapes as seen in silicon based microcantilevers.

Others describe microcantilevers made from photocurable expoxy materials SU-8: For this a planar process is needed, multiple levels are possible. Photolithography is necessary and the process is very near to the fabrication to silicon

cantilevers, also regarding the cost involved. An additional molding of nanostructures is possible. Tips with pyramidal shape have been molded, to achieve a Scanning Force Microscopy (SFM) like cantilever with a sharp tip (probe) able to scan over surfaces and record reliefs and images. SU-8 is a

material currently not very well specified, restricted in polymers, particularly if biocompatibility has to be assured. Other materials seem possible, including sol-gel materials.

Polymeric microdevices are fabricated with a so-called LIGA process, or assembly. These processes resemble those already described. Thin polymeric membranes with nanoimprint lithography have been fabricated, but thin membranes are rather difficult to be fabricated with injection molding. Foil like elements in a hot embossing process have been fabricated.

It is also possible to produce flexible foils which are

"fitted" or "molded" into cavities. An interesting application is the use of diffraction gratings instead of printed color on toys which make it possible to achieve an appropriate color effect by diffraction without using chemicals. The molds for LEGO bricks exhibit a surface pattern which is transferred to the LEGO brick. Thin Nickel molds have been used in injection molding machines to add a nanopattern onto dispensing systems using polymeric syringes.

Compact Disc injection molding uses as a standard thin Nickel shims which can be exchanged very fast. In production, shim copies rather than the original are used, and are replaced by another copy when degradation sets in. Instead of fabricating stamp copies in the same hard material as the original, in a specific nanoimprint lithography process developed by Obducat, intermediate polymer stamps are fabricated for every single imprint. This process, called intermediate polymer stamp

(IPS), is a two-step process, in which hot embossing onto a hydrophobic polymer foil, such as Zeonor or Topas, transfers the surface relief of the silicon, nickel, or polycarbonate original. These foils are used as molds in a simultaneously combined thermal and UV nanoimprint (STU) process, allowing the complete imprint sequence into UV-curable thermoplastic prepolymers to be performed at a constant temperature

isothermal process conditions. Using polymer stamps, either one-time use of the stamp or multiple use is possible.

Inmold labelling is very common in injection molding: a foil is used to be integrated and backfilled into a macroscopic part. Feeder mechanisms need to align the foil with respect to the mold. Sol-gel fabricated molds have been fabricated in a variety of ways, particularly interesting are hybrid molds which consist of a thin polymeric sol-gel relief in a resist on top of a metal backbone. The sol-gel relief is typically a few 10 nm thick up to several 100 μπι. Sol-gel materials used are

hydrogen silsesquioxane (HSQ) and so-called Ormocers .

Particularly Ormocers allow to integrate micro and

nanostructures with different heights. As a metal backbone nickel foils have been used with a thickness of a few 10 μπι to a few 100 μπι. Apart from metal, glass and polymer substrates can been used.

A surface corrugation is been used being based on stiffening of a membrane in a stencil setup, to enhance the stability of a perforated stencil agains deposition and stress. Cell growth and implants with surface topography is well explored. Most interesting are surfaces which enhance cell growth or even control the diversificaton of stem cells. A cantilever setup has been built which uses surfaces stress to enhance deflection of a beams. This setup will be used in the context of this patent application to detect the

deflection of cantilever beams. It is therefore the objective of the present invention to provide a micro-mechanical device that allows to implement an additional functionality in the cantilever- or membrane-like structure . The specific achievement and invention is a micromechanical device such as a micro-cantilever array or a micro-membrane which is fabricated using polymer injection molding, and which is patterend on one side with a micro- and nanorelief in a controlled way. The invention is based on the surface

patterning of an already finished mold insert by introducing a flexible patterned foil (here called "foil-like mold" or "foil stamp") onto the mirror side of a molding tools. The specific advantage is given if the foil stamp covers a large part of the mirror side because it serves both as a stamp and a sealing of the molding tool. It can also be applied from reel- to-reel as it is common in inmold-labelling processes. The microdevice according to the present invention is an element which comprises a body element of a few mm size and a thin membrane or cantilever like element which gains

additional functionality by incorporating a micro- or

nanopattern (either topography or chemical modification) on one side of the cantilever or membrane like part. The device is fabricated by micro-in ection molding with a

microfabricated or micromachined mold cavity. By using an additional foil-like mold, functionality is added to the microdevice without major modifications of its shape, outlines and volume. Thus mechanical and optical properties can be modified, simply by adding a device/element/ functionality (e.g. an optical diffraction grating, mechanical registration, ruler, fluidic channel, an tip or apex for profilometry) , a roughness (for controlling biological cell adhesion and growth) and selectivity (for selection by size, shape) . Also mechanical performance (stiffness, resonance frequency) can be modified by corrugations in the thin areas of the cantilevers or membranes. Due to the flexibility of the process,

modifications of the setup can be done easily with little effort, i.e. without fabricating a new mold. The invention is based on the method for surface patterning of foils.

Further advantageous embodiments for the device are as

follows :

(i) A device having surface corrugations with

appropriate size, depth, orientation on one side of the membrane or cantilever, to achieve a significant influence on its mechanical behaviour; e.g. stiffening, softening, defined resonance frequency and mode, engineering and control of mechanical parameters in an array for different cantilever beams in the same array. (ii) A device having surface patterns on one side of the membrane or cantilever with appropriate size, depth, orientation, to achieve a significant influence on biological cells to attach to the grooves and pillars and enable cell force measurements, either for

enhancement of attachment or for decrease or prevention of attachment, and for preferential direction of cell growth .

(iii) A device having surface patterns on one side of the membrane or cantilever with appropriate size, depth, orientation, to achieve a physical readout such as mirror with low roughness, lens, diffraction grating.

(iv) A device having surface patterns on one side of the membrane or cantilever with appropriate size, depth, orientation, to achieve a local thinning of the membrane or cantilever. Either without post-processing or with a post-processing step as e.g. a homogeneous thinning of the cantilever and membrane area by reactive ion

etching, the polymer in these depressions can be removed and holes or slits are created.

Explanation: In nanoimprint lithography the homogeneous thinning of polymer layers is used to generate windows to the underlying substrate. In contrast to this, a thinning of a suspended membrane or a cantilever with surface corrugations or local depressions results in a thinning of the overall membrane or cantilever. In the thinnest areas, this results in a local removal of material while other areas (which have been thicker) , stay intact. Thus perforated membranes can be generated, with opened holes; for the invention described here, a foil mold with high pillars would be used to add

depressions to the surface of the molded element. These depressions will result in holes after thinning, and the entire membrane can serve as a sieve.

A device having surface patterns on one side of membrane or cantilever with appropriate size, depth, orientation, to at least two of the effects mentioned in (i) to (iii) on the same cantilever, or on neighbouring cantilevers in the same array.

(vi) A device having one or more chemical substances on one side of the membrane or cantilever, to achieve a physical or chemical functionality, either by coating of the surface or by incorporating particles into the surface .

(vii) A device having a substance or part or all of a foil transferred onto the cantilever surface, which either serves as a permanent coating (metal, chemical, sol-gel, polymer, oxide or nitride) , or a temporary sealing, protective coating of the surface, a carrier on which the device is temporarily or permanently fixed. This can be done by delamination of a part of the foil stamp, or by transfer of the entire foil onto the device. A specific case is that of a selectively dissolvable stamp, i.e. a material as stamp which is dissolved in a solvent while the material of the cantilever stays unaltered. This enables to remove a stamp structure from the cantilever after opening of the molding machine and possibly also after demolding of the entire device. The aim is that structures can be demolded from the fragile cantilever without or with a reduced mechanical force, e.g. high aspect ratio structures.

Explanation: If the cantilever is modified by the foil on one side, which is coated with a silane etc., then due to transfer or diffusion during mold filling, a chemical surface modification can be achieved; e.g. a hydrophobic property can be achieved simply by applying a surfactant on the foil; in the same way, nanoparticles can be transferred, e.g. Si02 containing Ag for

sterilization purposes; in the same way, coatings or chemical agents could be transferred which enable a reaction with the polymer melt or with chemicals applied after molding; also chemicals for surface activation, crosslinking; Preferred examples of the fabrication process for the inventive micro-device are given below:

Placing the foil stamp into the injection molding tool:

(i) positioning/alignment and fixation of the foil stamp with respect to the molded device before closing the mold cavity of a injection molding tool, with preference on the on the mirror side of a mold cavity called

"mirror unit", the opposite part is called "mold insert unit"; in the present case, the mirror side is identical with the "injection side" of the molding tool, the opposite part is called or "clamping side"; the foil has to be positioned along the outlines of the cantilever beams or membranes;

If the positioning within an accuracy of 250 μπι

(micrometers), then patterns can be selectively placed on two neighboring cantilevers with distance of 250 μπι (micrometers) . Smaller and larger distances are possible (50 to 5000 μπι) , according to this, the needed accuracy is defined.

If the positioning within an accuracy of 10 μπι

(micrometers), then different patterns can be placed on the same cantilevers of 500 μπι (micrometers) length. Smaller and larger lengths are possible (50 to 5000 μπι) , according to this, the needed accuracy is defined. ii) The method comprising the mirror unit to contain an additional mold insert into which a foil stamp can be pressed by stretching; this is either done before closing the molding tool (using heating and pressure by air or mechanical pressure), or during injection;

iii) the mold is ready for the next injection step (from (iv) to (vii); here either the first foil stamp is used or a next is placed on the mirror side as described in (iii) .

Using delamination of a metal foil from a polymeric carrier a metallization can be generated, e.g. if gold is transferred from a carrier foil to the cantilever by delamination, no coating will be necessary; in the same way, electronic wires could be transferred;

Examples for the foil stamp fabrication are given hereinafter:

(i) embossing a thermoplastic or UV-curable foil with a micro- and/or nanostructured stamp with a stamp original in a thermal or UV- or combined thermal and UV-imprint processs; this structured foil is called "foil stamp";

(ii) release/demolding of the said foil from the stamp original by peeling and delamination of it; Injection molding process:

(iv) closing of the mold by pressing the mold insert unit onto the mirror unit, by this process, the cavity placed in the mold insert unit is closed and sealed; the foil is partly pressed between the flat sides of two

injection molding sides, but is free in the area of the cavity to enable the melt to flow onto it;

(v) injection of the viscous melt into the mold cavity through the injection gate and channels in the mold insert unit;

(vi) molding of all the outlines of the mold cavity in the mold insert; at the same time, the surface of the foil stamp is replicated, too;

(vi) opening of the mold tool after solidification of the molded micropart; the molded part is first released from the foil stamp and them ejected from the mold insert cavity; .

(vii) the mold is ready for the next injection step (from (iv) to (vii); here either the first foil stamp is used or a next is placed on the mirror side as described in (iii) .

Possible materials are disclosed below:

(i) Said foil can be a PC (polycarbonate) foil or

another thermoplastic polymer foil (typical thickness 10 to 250 μπι) , e.g. polysulfone (PSU) , cyclic olephine copolymer (COC) , poly ( etheretherketone ) (PEEK),

poly (propylene ) (PP) , polyoxymethylene copolymers (POM), cyclic olefin copolymers (COC) , polyvinylidenfluoride (PVDF) and liquid crystal polymer (LCP) ; poly ( ethylene- alt-tetrafluoroethylene) (ETFE) ; polyvinylalcohol (PVA) ;

(ii) The material can be a hybrid polymer such as sol- gel, Ormocer material;

(iii) The material can be a UV-cured and cross-linked

polymer such as expoxy (SU-8), polyimide (PI);

(iv) The material can be a non-thermoplastic polymer such as polytetrafluorethene (PTFE) ; polydimethylsiloxane (PDMS) , rubber;

(v) The material can be a photoresist on a carrier foil

(backbone) containing PMMA, SU-8, HSQ and sol-gel materials; the backbone may be made from metal (e.g. nickel, steel, aluminium, titanium, copper) , or polymer (COC, PI);

(vi) The material can be a thin metal film on a carrier foil (backbone) containing PMMA, SU-8, HSQ and sol-gel materials; the backbone may be made from metal (e.g. nickel, steel, aluminium, titanium, copper) , or polymer (COC, PI); or any other type of hybrid stamp where the backbone is flexible and the surface pattern hard against the polymer melt;

(vii) The material can be Si02, Si, Si3N4, A1203, diamond, graphite on a carrier foil (backbone) ;

(viii) Use of foils with inherent antisticking properties or with an antisticking film on top; Process modifications are the following options:

(i) The foil stamp can be already prepatterned by laser

machining .

(ii) The foil stamp can be pressed into a calotte on the

mirror side by pressure and during injection molding, thus enabling the fabrication of 3D patterns.

(iii) Both sides of the foil stamp are patterned, inducing a defined bending of the polymer stamp during injection.

(iv) The foil stamp can be composed of two materials with

different thermal expansion coefficients, resulting in defined buckling in contact with a hot mold or melt;

(v) The mirror unit or the mold insert unit can provide non- flat surfaces, which fit will into each other; the main issue of this patent is that a tight closing is

possible ;

(vi) The mirror unit can contain an additional mold insert into which a foil stamp can be pressed by stretching; this is either done before closing the molding tool (using heating and pressure by air or mechanical pressure), or during injection;

Preferred coatings and layers are the following:

(i) The foil stamp can be generated by extrusion;

(ii) The foil stamp can be coated by dispensing of

droplets, spraycoating, dipping, lamination;

(iii) The foil stamp can be patterned in a topological way by hot embossing;

(iv) The foil stamp can be patterned in a topological way by casting;

(v) The foil stamp can be patterned in a topological way by patterning with photolithography or electron beam lithography;

(vi) The foil stamp can be patterned in a topological way by etching, evaporation and lift-off, electroplating;

(vii) The foil stamp can be patterned in a chemical way by etching, evaporation and lift-off, electroplating, e.g. by using silanes or other materials chancing the wetting behaviour of the surface;

(viii) Several layers of photoresist with different

patterns, chemical composition or molecular weight can be used;

(ix) The photoresist can be a polymer plate and foil or thin film, which is laminated, e.g. by so-called

reversal imprint;

(x) The photoresist has a thickness with different resist heights from 30nm to 50 μπι;

Preferred methods for the foil stamp handling are: i) The foil stamp can be placed on the mirror unit, by gluing, lamination, clamping;

ii The foil stamp can be placed on the mirror unit, by spanning with a feeder (reel to reel) mechanism;

iii) The foil stamp can be placed onto the cavity onto the mold insert unit before injection, by spanning with a feeder (reel to reel) mechanism;

iv) The foil stamp can be placed onto the cavity onto the mold insert unit before injection, by lamination (from a substrate foil, e.g. provided by reel-to-reel) ; Preferred methods for injection molding are: i) The foil can be used to enhance the "tightening"

between the two mold units (leak proof) ; the softness of the molding foil enables a good leak tightness,

ii) The temperature of the mold (mirror unit) can be

chosen below the glass transition temperature of the foil stamp to avoid gluing and remelting/degradation of the stamp structures;

iii) The temperature of the mold (mold insert unit) can be chosen below the glass transition temperature of the foil stamp to avoid gluing and remelting/degradation of the stamp structures; iv) The temperature of the mold (mirror unit) can be alternatively chosen in the range or above the glass transition temperature of the foil stamp to enhance gluing and pattern transfer;

v) The temperature of the mold (mold insert unit) can be alternatively chosen in the range or above the glass transition temperature of the foil stamp to enhance gluing and pattern transfer;

vi) Additional alternatives could range the temperature being below or above glass transition temperature of the surface topography of a hybrid stamp; and within the range of the different glass transition temperatures of the top structure and carrier;

vii) The softness of the foil can be used for different purposes: Small details can be molded at the borders of the cantilever, i.e. the injection pressure of the melt is so high that the polymer can be squeezed into the structures which are between the flat surfaces of the mold units; thus surface structures can be generated which enlarge the cantilever area; furthermore this effect can be enhanced because the film is compressed and gaps can be generated in which thin films can be generated;

viii) The softness of the foil can be used for different purposes: Small details can be molded at the borders of the cantilever, i.e. the injection pressure of the melt is so high that the polymer can be squeezed into the structures which are between the flat surfaces of the mold units; soft molds can be deformed during molding, smaller structures with undercuts possible; this use of

"defects" can be even further enhanced if instead of a softened foil a flexible, elastic (rubber-like) foil is used . Preferred methods for the pattern transfer are:

A part of the foil stamp can be transferred by pattern transfer onto the injection molded part (e. the cantilever) as a transfer layer; this can be a coating, or a metallization, or surface topography, or microchannels for fluidics;

ii) A part of the foil stamp can be transferred by

pattern transfer onto the injection molded part (e.g. the body of the cantilever array) as a transfer layer; iii) A coating of the foil (e.g. a laminated surface

pattern or a patterned resist/metal) stamp can be transferred by pattern transfer onto the injection molded part, i.e. the cantilever or body of the

cantilever array;

iv) The gluing of the foils can be used for different purposes: a peeling during demolding due the flexibility of the foil stamp can enable better demolding which results in less damage, even with critital structures with undercuts or high aspect ratios; the foil stamps may stay sticking in molded part, which may help for sealing the surface of the final product or for

security;

v) Using delamination of a metal foil from a polymeric carrier a metallization can be generated, e.g. if gold is transferred from a carrier foil to the cantilever by delamination, no coating will be necessary; in the same way, electronic wires could be transferred;

vi) If the cantilever is modified by the foil on one

side, which is coated with a silane etc., then due to transfer or diffusion during mold filling, a chemical surface modification can be achieved; e.g. a hydrophobic property can be achieved simply by applying a surfactant on the foil; in the same way, nanoparticles can be transferred, e.g. Si02 containing Ag for sterilization purposes (see HeiQ) ; in the same way, coatings or chemical agents could be transferred which enable a reaction with the polymer melt or with chemicals applied after molding; also chemicals for surface activation, crosslinking; Typical process size ranges are: i) Polymeric cantilever normally have the following

dimensions (following the dimensions of typical silicon based cantilever array chips) . The cantilevers have lengths between 10 μπι and 2000 μπι, widths of 1 to 200 μπι, thicknesses of 1 to 100 μπι; the property which characterises a cantilever most is the aspect ratio, i.e. the ratio between its length and thickness (or sometimes width) . Cantilevers normally are defined a long beam with constant thickness and width over the entire length, emanating from the body to the tip.

Different forms exist, V-Shape, double cantilevers etc. for specific applications or enhancement of mechanical properites or areas, as long as one part of the beam is fixed and the other part can oscillate or bend freely. This patent applies for all possible forms.

ii) The cantilevers are normally fixed at a larger body.

The body has a length between 1 to 10 mm, widths of 1 to 10 mm, thicknesses of 0.2 to 1 mm; it is a macrocopic part which serves as a holder; in injection molding it is the part which will determine the amount of material to be used for the filling of the cavity; its surface normally contains electronics or other mechanical properties;

iii) Macroscopic surface corrugations, i.e. ridges with depths and widths in the range of a fraction of the cantilever thickness or width will have influence of the mechanical properties of the cantilever; e.g. 1 to 5 μπι deep trenches in 10 to 50 μπι thick cantilevers;

different depths and widths will enable to modify the mechanical properties of each cantilever in an array in a defined way;

iv) Micro- and nanoscopic surface corrugations, i.e.

ridges with depths and widths in the range much smaller than the cantilever thickness or width will have little influence of the mechanical properties of the

cantilever; e.g. lOOnm to 1 μπι deep trenches in 10 to 50 μπι thick cantilevers; however, they can be used to modify the selectivity of the cantilever surfaces or by generating a specific optical function like by

introducing a mirror like surface and a diffraction grating;

v) Apart from cantilevers, membranes can be patterned in the same way as cantilevers. In contrast to

cantilevers, where one part of the beam is fixed and the other part can oscillate or bend freely, membranes are composed of a thin entity which spans between at least two points of a body. This is either a bridge (a

cantilever with two fixed ends), or a large area of a thin films which is fixed at different locations of a body. This patent applies for all possible forms of membranes, as long as the presented process can be applied. In contrast to cantilevers, membranes are spanning over much larger areas, i.e. from 1 μπι to 20 mm. Preferred applications of the cantilevers are: i) Polymeric cantilevers, patterning of beam surface and surface of body for modification of mechanical stability; longitudinal (along the beam) deep line-like trenches or ridges will stabilize the cantilever beam; trenches and ridges orthogonal/perpendicular to the cantilever beam will make it less stiff; at least one trench or ridge will be patterned;

ii) Polymeric cantilevers, patterning of beam surface and surface of body with a pattern suitable for cell engineering; small (shallow) micro- and nanopatterns (line gratings, hole and pillars, pyramides, sawtooth structures, channels) will generate a defined surface roughness and enable, enhance or decrease growth of biological cells; measure cell force;

iii) Polymeric cantilevers, patterning of beam surface and surface of body with posts used as spacers; a convex pattern providing antiadhesive properties (avoiding gluing, as it can be seen for flat surfaces);

iv) Polymeric cantilevers, patterning of beam surface; single pillars, pyramids on the tip will enable to use them as scanning tips;

v) Polymeric cantilevers, patterning of beam surface; single holes, inverse pyramids on the tip will enable to use them as containers for liquids and particles;

vi) Polymeric cantilevers, patterning of beam surface; lens-like structures i.e. lenses with different shapes and profiles, e.g. aspherical lenses; convex and concave shapes, phase correction elements; combination of diffractive and refractive optics, mirrors will enable to direct light and split light;

vii) Polymeric cantilevers, patterning of beam surface; prism-like stuctures, will enable to couple light into waveguides, e.g. provided by the cantilever beam;

viii) Polymeric cantilevers, patterning of beam

surface; gratings will serve as calibration structures for AFM;

ix) Polymeric cantilevers, patterning of beam surface and surface of body with a pattern suitable for gas sensing; each cantilever will have a different pattern resulting in a different sensitivity for selectivity and comparison;

All applications are valid irrespective if only one

cantilever is patterned or many, also the body with an array of cantilevers (1 to 20 is included);

Membranes

i) Polymeric membranes, patterning of membrane surface and surface of body for modification of mechanical stability; longitudinal (along the beam) deep line-like trenches or ridges will stabilize the cantilever beam; trenches and ridges orthogonal/perpendicular to the cantilever beam will make it less stiff; at least one trench or ridge will be patterned; ii) Polymeric membranes, patterning of membrane surface and surface of body with a pattern suitable for cell engineering; small (shallow) micro- and nanopatterns (line gratings, hole and pillars, pyramides, sawtooth structures, channels) will generate a defined surface roughness and enable, enhance or decrease growth of biological cells; measure cell force;

iii) Polymeric membranes, patterning of membrane surface and surface of body with posts used as spacers; a convex pattern providing antiadhesive properties (avoiding gluing, as it can be seen for flat surfaces);

iv) Polymeric membranes, patterning of membrane surface; single pillars, pyramids on the tip will enable to use them as scanning tips;

v) Polymeric membranes, patterning of membrane surface; single holes, array of holes (sieves and stencils), inverse pyramids on the tip will enable to use them as containers for liquids and particles;

vi) Polymeric membranes, patterning of membrane surface; lens-like structures i.e. lenses with different shapes and profiles, e.g. aspherical lenses; convex and concave shapes, phase correction elements; combination of diffractive and refractive optics, mirrors will enable to direct light and split light;

vii) Polymeric membranes, patterning of membrane surface; prism-like stuctures, will enable to couple light into waveguides, e.g. provided by the membrane;

viii) Polymeric membranes, patterning of membrane surface; gratings will serve as calibration structures for AFM; ix) Polymeric membranes, patterning of membrane surface and surface of body with a pattern suitable for gas sensing; each cantilever will have a different pattern resulting in a different sensitivity for selectivity and comparison .

All applications are valid irrespective if only one membrane is patterned or many, also the body with an array of membranes (typically 1 to 20 membranes); All applications are valid irrespective if membranes and cantilevers are used in the same setup.

Preferred embodiments of the present invention are described hereinafter with more detail with reference to the attached drawings .

Figure 1 shows a molding tool (handy mold) with two sides (left side) . The mirror side contains the gate (top) and the location, where the patterned foil is placed (shown

schematically) . The clamping unit contains the mold insert (right side) with two mold cavities.

Figure 2 shows a top SEM micrograph with an array of eight laser ablated cantilever cavities in the steel mold insert. The cavity width varies from 80 to 130 μπι. The scale bar corresponds to 200 μπι. The SEM micrograph on the bottom is an image of an in ection-molded PP micro-cantilever array. Small tips at the cantilever end demonstrate the complete filling up to the venting channels.

Figure 3 is a real time monitoring of in ection-molded PVDF micro-cantilever deflection: Heat test of 30 μπι-thick micro- cantilevers with a temperature increase from 25 to 35 °C at a heating rate of about theat = 0.5 min and a temperature decrease back to 25 °C at a cooling rate of about t_COoi = 3.2 min .

Figure 4 shows a real-time monitoring of injection-molded PVDF micro-cantilever deflection in static mode. Formation of mercaptohexanol self-assembled monolayers on gold-coated 60 μπι-thick iCs .

Figure 5 illustrates in part (a) an optical micrograph of a replicated line grating patterns on 100 μπι-thick PC foil (period 10 μπι, depth 5 μπι) used as foil stamp, (b) and (c) SEM micrographs of the line pattern transferred during the μΙΜ process from foil to the surface of molded micro- cantilevers. In contrast to the non-patterned original beams, the surface patterned beams are slightly (10%) wider due to high injection pressure, the softness of the PC foil, and particularly because of the orientation of the grooves in the foil stamp.

Figure 6 shows SEM micrographs of PP micro-cantilevers with 1 μπι deep line corrugations (a) along, (b) perpendicular to micro-cantilever beams. In (b) different periods (period 4 and 10 μπι) are realized in adjacent beams. Rounding at the beam end is due to the fact that the venting channel at the end of the mold cavity is clogged in both cases.

A modular injection molding tool has been developed that comprises a quality steel cylinder (Polmax Uddeholm) 30 mm in diameter as mold insert with two internal resistive heating cartridges (Watlow Firerod, 230 V, 180 W, 49 W/cm²) fixed in the three-plate molding tool ^xhandy mold' with ejector pins (see Fig. 1, left side) . This setup enables us to proceed the vario-thermal heating scheme with short heating-up times to temperatures as high as 320 C in the vicinity of the mold cavities. The tool is installed in the clamping unit of an Arburg 320 Allrounder (Arburg, Lossburg, Germany) with a maximum clamping force of 600 kN.

The present mold system comprises only one cavity located on the closing side. The other side is free for mirror plates with designed micro- or nano-features .

The two parallel mold cavities (see Fig. 1, right side) were fabricated using laser ablation, and placed into the central part of the flat end of the cylinder. They are connected to the injection gate via a large plate-like cavity through 2.5 mm-wide gates for filling. The cantilever chip was designed with outlines of a micro-machined 500 μπι-thick silicon cantilever with a 3.5 x 2.5 mm² large body. It has eight 80 to 130 μπι-wide cantilever beams with a 500 μπι pitch on one side. The thickness chosen was usually in the range between 20 and 40 μπι. To guarantee fast and complete filling also molds with 60 μπι depth were applied (see Fig. 2, top micrograph) . For the venting, at the end of each beam cavity thin, 5 mm-long, 10 x 10 m²-wide channels were

incorporated. The polished steel plate with one injection gate is the flat counterpart opposite to the closing unit. Therefore, the upper side of each micro-cantilever beam has a polished finish (see Fig. 2, bottom micrograph) later used for laser beam reflection. Surface patterned beams require, thus, an additional mold insert with a micro- and nano- relief to be introduced at the mirror side. In place of another mold insert, we incorporate a thin, patterned polymer foil (see Fig.l, left side), i.e. the foil-like mold. This foil prepared by hot embossing, typically 25 to 100 μπι thick, forms the interface between the two units of the IM machine and is subjected to related pressure and heat. To ensure repeated alignment during injection and demolding, it is directly fixed onto the polished top by adhesive tape or clamps. The mold temperatures and pressures have to be low enough to enable a sufficient number of replications without degradation of the surface relief. The main advantage of the method lies in the simple integration of gratings with different sizes and orientations. It is particularly useful for test series. Even for mass

production the method is promising, since polymer membranes can be patterned in roll-to-roll processes.

The polymers used are different grades of

poly ( etheretherketone ) (PEEK: Solvay Advanced Polymer

AvaSpire AV-650 BG15, Solvay Advanced Polymer KetaSpire KT-

880NT, Victrex 150G) , poly (propylene ) (PP: Moplen SM 6100), polyoxymethylene copolymers (POM-C: 511P Delrin NCOIO), cyclic olefin copolymers (COC: Topas 8007X10),

polyvinylidenfluoride (PVDF: Kynar 720 Arkema) and liquid crystal polymer (LCP: Vectra A 390) .Up to 160 C, the tool temperatures were controlled by heated water. For the higher process temperatures up to 260 C oil served as heat

transport medium. The other process parameters are summarized in Table 1. As the foil mentioned above, 100 μπι- thick polycarbonate (PC: Bayer Makrofol ID 6-2) and 25 μπι- thick PEEK (Aptiv 2000 series) were inserted. While PC with a glass transition temperature of 148 C only allows molding polymers with rather low process temperatures, PEEK, which has a comparative glass transition temperature of 143 C was considered as higher temperature alternative because of its excellent demolding properties. The PC and PEEK membranes were hot embossed in a Jenoptik HEX 03 machine for a period of 10 minutes using temperatures of 160 and 175 °C and forces of 15 and 12 kN, respectively. As the molds for hot embossing, either silicon wafers or replicas in Ormostamp both with anti-sticking layer were used. Table 1. Injection molding process parameters for the selected polymer materials including all grades of PEEK.

COC PP PEEK POM-C LCP PVDF

Melt temperature 240 200 400 220 300 220

[°C]

Tool temperature 77 40 225 120 150 120

[°C]

Tool insert - - 260 - - - temperature [°C]

Injection speed 30 9 10 10 10 10

[cm³/s]

The injection-molded micro-cantilevers were coated on the mirror side with 20 nm-thin gold films using a thermal evaporator (Balzers BAE250) . This film guarantees sufficient laser beam reflectivity to use the Cantisens^® research system (Concentris GmbH, Basel, Switzerland) for measuring the deflection and the resonance frequency of the micro- cantilever .

Complete filling of the mold cavities was observed for all polymers (Fig. 2 left micrograph for PP) with the exception of PEEK, which needs higher processing temperatures than 260 °C. Also with the patterned foils, using standard isothermal micro-in ection molding process parameters, a complete filling of high-aspect-ratio micro-cavities was achieved for PP (see Fig. 2, bottom) . The mold temperature was low enough to use the polymeric foils for several hundreds replications without degradation of the surface relief .

With the exception of the high-performance polymer PEEK, which requires mold temperatures of up to 320 °C, the \iCs reveal the expected thermal behavior as demonstrated in the diagram in Fig. 3 for the gold-coated PVDF micro-cantilever under atmospheric conditions, i.e. in air, and in liquid (water) . The heat tests included a temperature cycle with an increase from 25 to 35°C and a subsequent decrease back to 25°C within a time of about four minutes. The heat tests prove the sensitivity of the micro-cantilevers that

corresponds to deflections of the order of 10 nm. The deflection signal exhibits an exponential, asymptotic behavior as confirmed by the fits in Fig. 3. For the temperature difference of 10 K the maximal deflection for

PVDF iCs in air corresponds to (95 ± 16) nm and (55 ± 5) nm for thicknesses of 30 μπι and 40 μπι, respectively. In water, these values should be similar but gave higher values, namely (127 ± 17) nm and (154 ± 55) nm) . Note the larger scattering of the data in liquid, which indicates less stable experimental conditions and reduced reproducibility in liquid compared to air.

The Cantisens^® Research system permits the experimental determination of resonance frequencies f_res and quality factors Q for the polymeric micro-cantilevers. Table 2 summarizes the mean values and related standard deviations of the resonance frequency measurements for the micro- cantilevers in air and water. The deviations of the

experimental data from the estimated ones are reasonably explained accounting for dimensional variations as well as the frequency dependence on E. The drop in resonance frequency in water results from the damping, which lowers the Q-factor of the micro-cantilevers as given in Table 2. The Q-factors were estimated directly from the frequency spectra .

Table 2. Mean values and related standard deviations of the resonance frequency f as well as quality factor Q in air and water.

micro-cantilever 30 μπι 40 μπι 30 μπι 40 μπι 30 μπι thickness and ΡΡ ΡΡ PVDF PVDF POM-C polymer

Frequency f in 48 ± 50 ± 1 60 ± 3 79 ± 5 60 ± 4 air [kHz] 3

Frequency f in 37 ± 33 ± 43 ± 5 52 ± 5 36 ± 7 water [kHz] 8 27

Theoretical - Eq. 38 46 66 88 78

Q-factor in air 28 46 38 19 33

Q-factor in water 20 11 10 9 19

As a first attempt towards biosensing, thiol bond formation on the iCs was recorded by means of the Cantisens^® Research system. The data of six PVDF 60 μπι-thick cantilevers from an in ection-molded array are shown in the diagram of Fig. 4. The deflection results from the surface stress, that is generated during the self-assembly of thiol molecules on the gold-coated substrate. Using the Stoney formula, the surface stress values can be determined to derive the sensitivity of the individual micro-cantilever sensors. Although the curves in Fig. 4 exhibit the expected characteristic behavior, the maximal amplitudes differ by up to a factor of three.

Stripe patterns in the beam cavities of the injection- molding tool have been applied to enhance the stability of the cantilevers and their stiffness against torsion. In order to guarantee stabilization, these corrugations need to be deep with respect to the cantilever thickness of 30 and 40 μπι, similar to stabilized membranes for stenciling. For this purpose, 5 μπι-wide, 5 μπι-deep stripes as presented in Figs. 5 and 6 were tested. Due to the orientation of the stripes, different effects were observed. For deep,

longitudinal stripes, a reduction of torsional oscillations was measured for some of the 40 μπι thick cantilevers.

However, due to the softness of the foil stamp and the orientation of the stripes the venting channels were closed, leading to incomplete filling and rounding of the beam apex. Therefore, these results are preliminary and need to be confirmed with fully molded beams. Complete filling was achieved if the venting channels were kept open (Fig. 5) . The inclined channels promote the complete filling of the mold cavities and, hence, give rise to longer cantilevers. For patterning of different patterns in adjacent beams, an alignment of some 10s of μπι of the patterns with respect to the beam outlines needs to be ensured (see Fig. 6) . This is particularly interesting for contractile cell force

measurements as cells generally orient themselves along the ridges. Therefore different orientations, depths and

patterns will be tested in the future. Long corrugations in membranes have been tested for

enhancement of stability and stiffening against torsion. Therefore long, 5μπι wide corrugations were considered as means to enhance the stability of the micro-cantilevers. In order to enable both stabilization and reflecting (the structuring is on the mirror side) , an alignment of 5 μπι precision needs to be ensured. The 1 μπι deep channels (see Fig 6) close the venting channel in case of

orthogonal/perpendicular orientation but leave the venting channel open in the longitudinal case. Longitudinal channels promote complete filling of the mold cavities giving rise to longer cantilevers. Moreover longitudinal channels are preferred for the contractile cell force measurements as cells orient themselves along ridges, lines.

Claims

Claims

1. A micro-device which comprises a body element of a few mm size and a thin membrane or cantilever-like element which gains additional functionality by incorporating a micro- or nanopattern (either topography or chemical modification) on one side of the cantilever- or membrane-like element;

said micro-device being fabricated by micro-in ection molding with a microfabricated or micromachined mold cavity;

whereby an additional foil-like mold is used and functionality is added to the micro-device without modifications of its shape, outlines and volume resulting in mechanical and optical properties that are modified by adding the additional

functionality being selected from a group consisting of an optical diffraction grating, a mechanical registration, a ruler, a fluidic channel, an apex for profilometry, a hole or a multitude of holes, a roughness for controlling biological cell adhesion and growth and selectivity for a selection by size and/or shape) ; whereby also mechanical performance such as its stiffness and/or its resonance frequency is modified by corrugations in thin areas of the cantilever- or membrane-like elements .

2. The device of claim 1, having surface corrugations with appropriate size, depth, orientation on one side of the membrane- or cantilever-like element, to achieve a significant influence on its mechanical behaviour; e.g. stiffening, softening, defined resonance frequency and mode, engineering and control of mechanical parameters in an array for different cantilever beams in the same array.

3. The device of claim 1 or 2, having surface patterns on one side of the membrane- or cantilever-like part with appropriate size, depth, orientation, to achieve a significant influence on biological cells to attach to the grooves and pillars and enable cell force measurements, either for enhancement of attachment or for decrease or prevention of attachment, and for preferential direction of cell growth.

4. The device of any of the preceding claims, having surface patterns on one side of the membrane- or cantilever-like part with appropriate size, depth, orientation, to achieve a physical readout such as a mirror with low roughness, a lens, a diffraction grating, or a prism.

5. The device of any of the preceding claims, having surface patterns on one side of the membrane- or cantilever-like part with appropriate size, depth, orientation, to realize at least two of the effects mentioned above on the same cantilever, or on neighbouring cantilevers in the same array.

6. The device of claim 1, having one or more chemical

substances on one side of the membrane- or cantilever-like part, to achieve a physical or chemical functionality, either by coating of the surface or by incorporating particles of a different material into the surface or attachment onto the surface .

7. The device of any of the preceding claims, having surface patterns on one side of the membrane- or cantilever-like part, on the flat side the body element, with appropriate size, depth, orientation, to add a surface pattern used for the identification of the element by using a diffraction grating, a bar code, a number or letter or any kind of pattern

detectable by optical or mechanical means.

8. The device of any of the preceding claims, having a

substance or part or all of a foil transferred onto the surface of the cantilever or membrane like surface, which either serves as a permanent coating (metal, chemical, sol- gel, polymer, oxide or nitride) , or a temporary sealing, protective coating of the surface, a carrier on which the device is temporarily or permanently fixed whereby this is done by delamination of a part of the foil stamp, or by transfer of the entire foil onto the device or alternatively a specific case is that of a selectively dissolvable stamp, i.e. a material as stamp which is dissolved in a solvent while the material of the cantilever- or membrane like element stays unaltered enabling to remove a stamp structure from the cantilever- or membrane like element after opening of the molding machine and possibly also after demolding of the entire device having the aim that its structure can be

demolded from the fragile cantilever- or membrane-like element without or with a reduced mechanical force, e.g. high aspect ratio structures.