Masayuki Sohgawa

Tactle array sensor with inclined chromium/silicon piezoresistive cantilevers embedded in elastomer

Tactile array sensor of the micro-cantilevers embedded in the elastomer has been fabricated to detect normal and 2-axes shear stresses. It is demonstrated that tactile array sensor with 3 × 3 detective elements can be fabricated with excellent yield. The sensor element is sensitive to both normal and shear stresses applied on entire sensor surface. Moreover, it has good directional characteristics so that it is shown that magnitude and direction of shear stress can be obtained by difference of output voltages of adjacent sensor cantilevers. The sensor output has good reproducibility for multiple measurement. The output from sensor element drastically changes with shifting applying position of force. It is considered that we can obtain pressed position from distribution of output from sensor element array.

Crosstalk Reduction of Tactile Sensor Array with Projected Cylindrical Elastomer over Sensing Element

A tactile sensor array covered by a projected cylindrical elastomer has been designed and fabricated for crosstalk reduction among sensor elements caused by the lateral deformation of the elastomer. The analysis of elastomer deformation by the finite element method showed that the optimal thickness of the flat elastomer between cylinders and the substrate is 50–100 µm, because the sensor structure has not only a low crosstalk but also a high robustness. A tactile sensor array having the flat elastomer of 70 µm thickness has little crosstalk and high robustness.

Fabrication and Characterization of Silicon-Polymer Beam Structures for Cantilever-Type Tactile Sensors

Silicon-fluoropolymer beam structures for cantilever-type tactile sensors have been fabricated and characterized. Curvature shape and tip height of fabricated cantilever agree well with theoretical calculated results. The deposition condition of polymer layer has been optimized in terms of process yield and tip height. The optimal thickness and curing temperature are 4-5 mum and 200degC for 1.5 mum thick Si, respectively. The response of the tactile sensor with PDMS elastomer has been investigated against pressure. Although resistance of the platinum strain gauge has large temperature drift, it is obviously proportional to pressure, so that it becomes evident that the pressure can be detected by tactile sensor embedded in the elastomer.

Fabrication and Characterization of Normal and Shear Stresses Sensitive Tactile Sensors by Using Inclined Micro-cantilevers Covered with Elastomer

The tactile sensors for human support robots which can detect both normal stress and shear stress and have human-friendly surface have been proposed. Micro-cantilevers adequately inclined by Cr deflection control layer were fabricated by the surface micromachining on SOI wafer. The cantilevers were covered with the PDMS elastomer for human-friendly surface. When the stress is added to the surface of elastomer, the deformation of cantilevers along with elastomer is detected as piezoresistive layer in the cantilevers. The piezoresistive response of the cantilever is analyzed by FEM calculation. The response of the fabricated tactile sensor to normal stress and shear stress was measured by output from this resistance. The tactile sensor with PDMS elastomer can detect both normal stress and shear stress. On the other hand, it hardly has sensitivity to shear stress of orthogonal direction to the cantilever. It means that the tactile sensor can distinguish the direction of shear stress. The sensitivity of tactile sensor vary widely with cantilever pattern and relation between direction of cantilever and crystallite orientation of Si. It is suggested that the sensitivity of tactile sensor can be improved by using FEM estimation and selective ion implantation.

Nondestructive and Contactless Monitoring Technique of Si Surface Stress by Photoreflectance

Strain and stress at the Si surface have been studied by photoreflectance (PR) spectroscopy. A Si diaphragm structure has been fabricated in order to produce the surface strain caused by N2 gas pressure which changes the PR spectra of the Si diaphragm. The transition energy obtained from the PR peak energy of approximately 3.4 eV is proportional to the surface stress, which is calculated by elastic analysis. Additionally, PR spectroscopy was applied to measure stress at the interface between the Si and thermal oxide. As the SiO2 growth temperature increases, the interface stress decreases. From our experimental results, it is considered that PR spectroscopy is effective as a contactless and nondestructive monitoring technique for Si surface stress.

Multimodal measurement of proximity and touch force by light- and strain-sensitive multifunctional MEMS sensor

A multimodal sensor with Si micro-cantilever embedded in PDMS elastomer for measurement of proximity and touch forces has been fabricated and characterized. DC resistance of the strain gauge on the cantilever changes in proportion to the indentation depth of the object. On the other hand, the AC (> 0.5 MHz) impedance including photo-sensitive component of Si increases with increase of distance between the sensor surface and the object because of decrease of light intensity reflected on the object surface. Moreover, the AC impedance is different between grounding and floating of the proximate object because of difference of distribution of electrostatic field between electrodes, so that it is suggested that proximity can be detected as the impedance change by light as well as the electric field.

Fabrication and Noise Reduction of the Miniature Tactile Sensor Using Through-Silicon-Via Connection with Signal Amplifier

A miniature tactile sensor has been fabricated by connecting stress-sensitive part with an amplifier of integrated circuit through through-silicon-via (TSV) electrically. The sensitive part consists of three warped cantilevers with piezoresistive NiCr thin film which are prepared on a silicon-on-insulator wafer by the surface micromachining technique. The TSV connection can reduce noise of detected change of the piezoresistive output induced by wire between the sensitive part and the amplifier. Fabricated tactile sensor of 5×5 mm2 size has linear dependence of the output on both normal and shear forces. The output noise has been successfully decreased by 14 and 34% in the sensor using the TSVs compared with that using wires of 3 and 6 mm lengths, respectively.

Studies on Curvature Deformation Control of Bilayer Cantilever Fabricated by Surface Micromachining of SOI Wafer

Cr/Si bilayer cantilevers for an integrated multi-axis tactile sensor were fabricated by Si surface micromachining process. Among the cantilevers with various shapes, the rectangular and semicircular cantilevers were deflected upward with good controllability. The maximum deflections were compared with those calculated by the finite element method. Calculated deflections of Cr/Si cantilevers agree considerably with the experimental results. So, it is considered that the analysis by finite element method is useful to optimize layer thickness and size to obtain Cr/Si bilayer cantilevers with accurate deflection.

Identification of various kinds of papers using multi-axial tactile sensor with micro-cantilevers

Various kinds of papers have been identified by active touch of a multi-axial tactile sensor which has micro-cantilevers with strain gauge film on Si. When fine surface of the standard surface roughness scale and the printed stripe pattern on a banknote have been scanned by the tactile sensor, it allows to measure such fine roughness as a resistance change of the gauge film, and the triangular unevenness could be obtained down to 20 μm. Transient responses of the resistance change have been obtained when the sensor was pushed and moved on various kinds of blank papers successively. Some features are extracted from the response by a principal component analysis and the papers are classified in four clusters.

Fabrication of a Flexible Array for Tactile Sensors with Microcantilevers and the Measurement of the Distribution of Normal and Shear Forces

A Tactile sensor system consisting of elements with three microcantilevers embedded in a cylindrical elastomer has been fabricated by micro electromechanical systems (MEMS) technology. These sensor small size (3 ×4 mm2) chips are mounted on a flexible sheet, and thus the fabricated sensor array can be set even on a curved surface. In addition, the spacial distribution of normal and shear forces is obtained when two kinds of objects (an acrylic hemisphere and a brass cylinder) come in contact with the fabricated sensor shifted laterally. The distribution results appropriately reflect the surface shape of the object and give the behavior of the forces vector.