MEMS Force Sensors Research Articles

Paper-based piezoresistive MEMS sensors

This paper describes the development of MEMS force sensors constructed using paper as the structural material. The working principle on which these paper-based sensors are based is the piezoresistive effect generated by conductive materials patterned on a paper substrate. The device is inexpensive (∼$0.04 per device for materials), simple to fabricate, lightweight, and disposable. Paper can be readily folded into three-dimensional structures to increase the stiffness of the sensor while keeping it light in weight. The entire fabrication process can be completed within one hour without expensive cleanroom facilities using simple tools (e.g., a paper cutter and a painting knife). We demonstrated that the paper-based sensor can measure forces with moderate performance (i.e., resolution: 120 μN, measurement range: ±16 mN, and sensitivity: 0.84 mV mN(-1)). We applied this sensor to characterizing the mechanical properties of a soft material. Leveraging the same sensing concept, we also developed a paper-based balance with a measurement range of 15 g, and a resolution of 0.39 g.

MEMS-based power disconnect for <inline-formula><math display="inline" overflow="scroll"><mrow><mn>42</mn><mtext>-</mtext><mi mathvariant="normal">V</mi></mrow></math></inline-formula> automotive power systems

We present the design of a micro-electro-mechanical-system(MEMS)-based power disconnect for use with the proposed 42-V automotive power systems. High-voltage power systems are prone to arcing, which occurs during power disconnections. The high arcing current may lead to severe damage on the systems and may expose electric shock hazards to humans. The objective of the MEMS-based power disconnect we propose is to eliminate arcing occurrence in the systems. To eliminate arcing, one alternative is to electronically terminate the power supply to the system prior to the physical disconnection. The integrated MEMS force sensor on the power disconnect will be activated as a service technician disconnects the connector. The power supply to the system will be electronically shut off to prevent arcing during the physical interruption. The MEMS force sensor on the disconnect has an overall dimension of 3600 μm××1000 μm×10 μm and is fabricated with the Micragem fabrication process. A displacement reduction mechanism is incorporated into the sensor design to increase the sensitivity of the force sensor. Results show that the sensor is capable of measuring a maximum force input of 10.7 mN, resulting from a 20-μm displacement on the sensing structure.

A miniaturized and flexible optoelectronic sensing system for tactile skin

This paper describes the development of a hybrid sensing module consisting of a general purpose electro-optical converter and three MEMS force sensors integrated into flexible substrates for tactile skin applications. The features of the converter, namely its flexible and thin substrate and small dimensions, programmability, optical coding and transmission of the information allow this versatile device to host different sensors, locally preprocess signals, translate this diverse information into a ‘common language’, and transmit it in a parallel, efficient and robust way to the processing unit. After discussing the major technical requirements, the design of the sensing, electrical and optical subsystems is illustrated, as well as the whole process for the module fabrication. A first characterization of a working prototype, hosting three MEMS force sensors and nine independent optical channels was performed. The global performance in terms of sensitivity, bandwidth and spatial sensing resolution make the presented module suitable to be used as basic element of a complete tactile system, conceived for robotic grasping and manipulation. Several solutions for mass production, improved optical properties and more efficient optical transmission are discussed.

Fabrication and characterization of folded SU-8 suspensions for MEMS applications

A novel wafer-level fabrication technique for polymeric springs combined with a silicon proof mass is presented for applications in MEMS force sensors or scanning micromirrors. Furthermore, passive test structures for the determination of mechanical parameters of the polymer are integrated on the wafer during device fabrication. The test structures allow for chip scale process monitoring in respect to the material parameters. The large difference of material stiffness and thickness between the springs and the proof mass concentrates the entire mechanical deformation into the springs. Furthermore, the polymeric springs can be used as electrically isolated suspension for electrostatically levitated devices. Devices have been fabricated and characterized by means of frequency response analysis. Thereby, a polymeric suspension with a spring constant of 8.7 N/m is presented, while the suspended structure itself features a spring constant of 140 kN/m. Material properties of the spring material (SU-8 2025) were measured to be 2.45 ± 0.6 GPa, 27.2 ± 2.2 MPa and 13.8 ± 3.2 MPa/m, for Young's modulus, the residual stress and the residual stress gradient, respectively.

2P2-B13 MEMSフォースセンサを用いたソフトフィンガ型触覚デバイスの開発と接触実験

2P2-B13 MEMSフォースセンサを用いたソフトフィンガ型触覚デバイスの開発と接触実験

Design and modeling of a MEMS pico-Newton loading/sensing device

In this paper we present a novel MEMS force sensor that exploits the post-buckling phenomenon of slender silicon columns. The design philosophy and fabrication process is discussed and analytical expressions for the force-displacement characteristics are developed. The sensor can be used to perform quantitative and qualitative measurements in-situ in SEM, TEM or STM, where the small chamber size makes it challenging to integrate conventional force-displacement sensors. Potential applications for the sensor are characterization of carbon nanotube-polymer interfaces, nanoscale thin film testing and mechanical testing of single biological cells.

Application of MEMS force sensors for in situ mechanical characterization of nano-scale thin films in SEM and TEM

Abstract We present a novel tensile testing technique utilizing MEMS force sensors for in situ mechanical characterization of sub-micron scale freestanding thin films in SEM and TEM. Microfabrication techniques are used to cofabricate the thin film specimens with force sensors to produce the following unique features: (1) small setup size to fit in SEM and TEM for in situ experiments, (2) ability to measure tensile pre-stress in specimen, (3) alignment between specimen and applied loading axes with lithographic precision, (4) no extra gripping mechanism required, and (5) ability to measure creep strain in the material. The technique allows single or multilayers of materials that can be deposited/grown on silicon substrate to be tested. We demonstrate the technique by testing a 100 nm thick, 8.8 μm wide and 275 μm long freestanding aluminum specimen (average grain size about 50 nm) in situ inside an environmental SEM chamber, and present another setup for similar experiment in TEM. Experimental results strongly suggest that at this size scale: (1) elastic modulus does not change, (2) size effects on yield strength are pronounced (63 times the bulk pure aluminum yield stress), and (3) permanent strain hardening effects are absent.

In-Situ Mechanical Characterization of a Freestanding 100 Nanometer Thick Aluminum Film in SEM Using MEMS Sensors

ABSTRACTWe present the uniaxial stress-strain response of a freestanding 100 nanometer thick 99.99% pure sputtered Aluminum film with grain size about 60 nanometers, tested in-situ inside a SEM chamber. The specimen is cofabricated with MEMS force and displacement sensors to minimize the experimental setup size, allowing both quantitative and in-situ tests to be performed in SEM and TEM chambers. The experimental results strongly suggest that at this size scale, a) Elastic modulus remains same as the bulk Aluminum, b) Yielding starts at about 625 MPa, and c) Strain hardening effect is absent, which indirectly suggests the deformation at this size scale is not dislocation mechanism based.