WO2008106813A1

WO2008106813A1 - Sensor made of organic materials for the measurement of mechanical variables and the subsequent evaluation thereof

Info

Publication number: WO2008106813A1
Application number: PCT/CH2008/000082
Authority: WO
Inventors: Udo Lang; Jürg Dual
Original assignee: Eth Zurich
Priority date: 2007-03-02
Filing date: 2008-02-29
Publication date: 2008-09-12

Abstract

The invention relates to a sensor, which is made of organic materials and can be used for the measurement of static and dynamic mechanical variables. Accelerations are measured by means of a strain gauge beam 1 having a seismic mass 2 at the end, wherein both are made of a flexible polymer. Due to the inertia of the seismic mass, the beam is deflected, resulting in expansion in the edge of the strain gauge beam 1, wherein the expansion can be measured by means of an intrinsically conductive polymer 3 that is structured into a strain gauge. The further modules 4, which comprise a measurement bridge, an amplifier circuit, a transmitter, and an optical display, or electrodes, are integrated on the substrate 5. A frame 6 may also be provided, which simplifies the handling of the overall system and may protect the strain gauge beam from lateral influences. The substrate 5 and the frame 6 are made of the same flexible polymer as the strain gauge beam 1 and the seismic mass 2.

Description

Sensor consisting of organic materials for measuring mechanical quantities and their subsequent evaluation

The present invention relates to a sensor for measuring dynamic and static mechanical magnitudes according to the preamble of claim 1, to a method for its production and to a use according to claim 5.

The present invention is concerned with the measurement of dynamic and static mechanical magnitudes. As shown in principle in FIG. 1, the signal supplied by the sensor can be transmitted by means of a measuring bridge (Wheatstone bridge) and an amplifier to a transmitting device for wireless reading by external reading devices, to a display or only to tapping contacts. All modules of the system shown in FIG. 1 are said to consist of organic materials due to the general advances in the field of organic electronics.

FIG. 2 shows how accelerations can be measured with the aid of a bending beam 1 with seismic mass 2 at the end. Due to the inertia of the seismic mass, the beam 1 is deflected, which leads to strains in the edge, which can be measured by an intrinsically conductive polymer 3, which is structured meandering into a strain gauge (DMS). The further modules 4 shown in FIG. 1, which comprise a measuring bridge, an amplifier and a transmitting device, an optical display or electrodes, can be integrated on the substrate 5. In addition, a frame 6 can be provided which simplifies the handling of the overall system and can protect the bending beam against mechanical influences in the substrate plane. FIG. 3 shows a possibility for measuring pressures. In this case, a membrane 7 is deformed by pressure differences, which leads to strains on the membrane surface, which in turn can be measured with a DMS. The sensor effect is based in both cases on the piezoresistive effect in electrical conductors. In this case, the elongation changes the length and cross-sectional area and thus also the resistance. In the present invention, the piezoresistive effect is to be exploited in intrinsically conductive organic conductors. For this purpose, the document US Pat. No. 5,505,093 discloses a process with which, on the one hand, solvent-based intrinsically conductive polymers, such as polyaniline, can be structured into DMS. On the other hand, non-intrinsically conductive solvent-based polymers such as polystyrene are partially rendered conductive by ion implantation. The production of lateral structures in the micron range takes place by means of photoresist layers as masking layers and subsequent dry etching by means of reactive ion etching.

In recent years, progress has been made in the field of intrinsically conductive polymers as well as organic semiconductors to become functional electronic ones

To manufacture circuits for radio tags completely from these materials [1, 2].

The primary objective of this research is to produce these RFID tags for wholesalers to identify individual goods. Through the use of organic

Materials and processes for mass production, such as printing presses, which allow roll-to-roll production, can offer extremely low prices to the individual

RFID tags are achieved. However, no sensor elements are integrated yet.

The present invention therefore has for its object to provide sensors for measuring mechanical magnitudes, which can be combined with elements for evaluation to form a new overall system. In order to achieve a low-cost production, such materials and methods are to be used, which are compatible with the aforementioned radio tags. This is achieved by sensors having the features designated in claim 1. By embedding mechanical sensors for measuring dynamic or static mechanical magnitudes, it is possible to check, for example, during shipment of packages with sensitive contents, whether inadmissible stresses such as falls or impacts have occurred on the transport path when the system is to measure accelerations according to claim 10. For pressure-sensitive goods, the system can also be used according to claim 10. Another application of the sensors is in the field of "wearable computing", ie the integration of sensors and electronics in garments, where the sensors could be integrated in large-area films and then used as a tactile film for detecting objects. The invention will be explained in more detail with reference to the drawing. 1 shows a block diagram of the basic mode of operation when the sensor is in a

Entire system is embedded

Figure 2 Bending beam sensor with possible integration in the overall system Figure 3 membrane sensor with possible integration in the overall system

FIG. 4 process flow of production:

1. Substrate structuring

2. Layer structuring Figure 5 Process flow of production: 1. Layer structuring

2. Substrate structuring

FIG. 6 structuring of the substrate by laser or water cutting

Figure 7 structuring of the substrate by photolithography

FIG. 8 Structuring of the Substrate by Punching FIG. 9 Membrane Production

FIG. 10 Microstructuring of intrinsically conductive polymers by so-called lift-off

FIG. 11 Microstructuring of intrinsically conductive polymers by inkjet printing

FIG. 12 Microstructuring of Intrinsically Conductive Polymers by Imprinting FIG. 13 Microstructuring of Intrinsically Conductive Polymers by Printing Methods

FIG. 14 Microstructuring of Intrinsically Conductive Polymers by Vapor Deposition

The manufacture of the sensor is shown schematically in FIGS. 4 and 5. A first possibility consists in firstly structuring the substrate 5 and then first applying the organic functional layers 3 and 4; the second possibility is the reverse process order. The substrate 5 may consist of thermoplastic polyesters such as polyethylene terephthalate (PET) or polyimide (PI), for example, but is not limited thereto. However, when selecting the substrate material, it must be ensured that it has sufficient flexibility to be used for roll-to-roll production.

FIG. 6 shows a first variant for structuring the substrate 5

Waterjet or laser cutting 8 on corresponding CNC-controlled machines from a corresponding film a bending beam 1 with seismic mass 2 at the end and a larger substrate surface 5 for later application of the electronics. 4 cut out.

FIG. 7 shows a possible structuring of the substrate 5 when the substrate 5 consists of photolithographically structurable polymers such as the polyimide PI 2723 from HD Microsystems GmbH (Bad Homburg, Germany). The polymer is first applied to another auxiliary substrate 9. Methods for this purpose are distributing by means of a doctor blade or pipetting up and then allowing to run. The auxiliary substrate must be flexible so that it can also be used in printing presses in a roll-to-roll process. In order to define the shapes, a mask 10 is required which covers the areas not to be exposed during the irradiation with UV light 11. Subsequently, it is developed with a developer solution, whereby the later form stops and other areas are removed. The auxiliary substrate 9 should be chosen so that it also dissolves in the developer and thus only the main substrate 5 stops.

FIG. 8 shows the possibility that the mold 1, 2 is defined by punching out of the substrate 5 with the aid of a correspondingly shaped tool 12. In order to allow roll-to-roll production, material which later does not belong to the substrate 5 is punched out.

Figure 9 shows a roll-to-roll fabrication compatible method of making a membrane. For this purpose, a heated stamp 13 is pressed into the flexible thermoplastic substrate 5 so far that the softened polymer is partially displaced until only a thin layer remains and thus creates a membrane.

The previous steps involved the structuring of the substrate 5. The structuring of the sensitive material 3 will be described in the following steps. As a sensitive material, the intrinsically conductive and in aqueous dispersion present poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate (PEDOT / PSS) or other intrinsically conductive polymers can be used.

FIG. 10 shows a structuring option if the intrinsically conductive polymer 3 and the substrate 5 can not be dissolved in organic solvents. This is the case, for example, with PEDOT / PSS. The method used is in the field of In the process, a photoresist layer 14 is first photolithographically patterned on the substrate and subsequently the intrinsically conductive polymer 3 is deposited by spin-coating, spray coating or pattering, after drying the layer either in air or by heat As with a hot plate or a hair dryer, the layer composite is immersed in organic solvent, whereby the photoresist areas 14 and other layers located thereon are dissolved in. The said method was presented in [3].

Figure 11 shows another possibility. As demonstrated in [4], the intrinsically conductive polymer 3 can also be deposited as defined by an ink jet printer 15. It is a cost effective method because complicated photolithography steps can be dispensed with.

FIG. 12 shows another cost-effective way of depositing. In this case, a structured stamp 16, for example of polydimethylsiloxane (PDMS), immersed in a bath with the intrinsically conductive polymer 3 and then pressed onto the substrate 5. As a result, the structures are impressed on the substrate.

Figure 13 shows a process which is very suitable for roll-to-roll production. In this case, the structures are printed on the substrate 5 by, for example, a cylinder 17 using standard printing methods such as flexographic printing, offset printing, gravure printing or screen printing. Wireless tags without sensor function produced by this method will be launched in the near future by PoIyIC (Fürth, Germany).

The structuring possibilities of an intrinsically conductive polymer shown in FIGS. 10-13 and the utilization of a piezoresistive effect in this intrinsically conductive polymer mentioned in claim 1 distinguish this invention from the previously mentioned document US Pat. No. 5,505,093 in which DMS is prepared by dry etching and ion implantation be described from.

FIG. 14 shows a structuring possibility for organic substances whose molecules consist only of short chains and can thus be vaporized. By using a shadow mask 18, areas of the substrate 5 to which no material is to be vapor-deposited are covered. Another possible structuring of the intrinsically conductive polymer 3 results when the substrate material 5 is transparent to Nd-YAG laser. In [5] it is described how structures made of PEDOT / PSS can be produced by Nd.ΥAG laser cutting.

The previous embodiments have shown the variant of the process sequence shown in FIG. The other variant in FIG. 5 is based on first applying one of the possibilities shown in FIGS. 10-14 for structuring the intrinsically conductive polymer 3 and then, in a second step, one of the possibilities for structuring the substrate shown in FIGS 5th

List of reference numbers and abbreviations used

1 bending beam

2 seismic mass

3 intrinsically conductive polymer

4 modules: measuring bridge; Amplifier; Transmitter, display or contacts

5 flexible substrate

6 frames

7 membrane

8 water or laser beam

9 auxiliary substrate

10 mask

11 UV light

12 punching tool

13 stamps

14 photoresist layer

15 inkjet printer

16 stamps

17 impression cylinder

18 shadow mask

List of abbreviations used

Strain gauge strain gages

PET polyethylene terephthalate

PI polyimide

PEDOT / PSS poly (3,4-ethylenedioxythiophene) / polystyrenesulfonate

PDMS polydimethylsiloxane Bibliography

[1] Cantatore, E. et al .: A 13.56 MHz RF ID System based on Organic Transponder, ISSCC 2006, San Francisco, USA.

[2] Rost, H .: From Polymer Transistor to Printed Electronics, PLASTICS-PLAST EUROPE 95 (10): 209-214 2005.

[3] Lang, U. et al .: Fabrication of a tensile test for polymer micromechanics, Microelectronic Engineering 83 (2006) 1182-1184.

[4] Sirringhaus, H. et al .: High-Resolution Inkjet Printing of All-Polymer Transistor Circuits, Science 290 (2000) 2123-2126.

[5] Lang, U., Dual, J .: Mechanical properties of BAYTRON P, 4 ^th IEEE International Conference on Polymers and Adhesives in Microelectronics and Photonics POLYTRONIC 2004, Portland (USA), 12-15. Sept. 2004, pp. 230-236, ISBN: 0-7803-8744-9.

Claims

claims

1. sensor having a mechanically deformable element, characterized in that the deformable element is a composite layer of organic materials, of which at least one has a piezoresistive effect, in the form that the electrical resistance of this organic material in the deformation of the layer composite changes.

2. Sensor according to claim 1, characterized in that the organic material is an intrinsically conductive polymer.

3. Sensor according to claim 2, wherein the intrinsically conductive polymer is poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate.

4. Sensor according to one of the preceding claims, characterized in that the piezoresistive organic material is structured by a standard printing method, such as flexographic printing, offset printing, gravure printing, inkjet printing or screen printing.

5. A method for measuring mechanical, static and / or dynamic variables, which uses a sensor, a measuring bridge and / or an amplifier circuit and a module for evaluation, characterized in that it contains a sensor according to one of the preceding claims.