Toshiyuki Toriyama

Super-long life tension–compression fatigue properties of quenched and tempered 0.46% carbon steel

Abstract To investigate the effect of non-metallic inclusions on fatigue properties of quenched and tempered 0.46% carbon steel (HV≅650) in super-long life fatigue range (107≤N≤5.0×108), tension–compression fatigue tests were carried out. The fatigue strength was discussed based on the area parameter model. The results obtained are: 1. Fatigue fracture origins were mostly at a non-metallic inclusion. 2. However, the location of the inclusion at fracture origin were not uniformly distributed over the specimen section due to the non-uniform distribution of residual stress induced by heat treatment. 3. The fatigue limit by the cycle N=5.0×108 can be predicted by the area parameter model, i.e. with three parameters, the Vickers hardness, HV, of the matrix, the square root of the projected area of inclusions, area , and residual stress. 4. The expected value of inclusion size area max of 0.46% carbon steel in a definite number of specimens can be estimated using the statistics of extreme values. The lower bound of the scatter of fatigue strength was predicted with the combination of the area parameter model and the value of area max .

Single crystal silicon nano-wire piezoresistors for mechanical sensors

A p-type silicon (Si) nano-wire piezoresistor, whose minimum cross-sectional area is 53 nm/spl times/53 nm, was fabricated by combination of thermal diffusion, EB (electron beam) direct writing and RIE (reactive ion etching). The maximum value of longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor was found to be 48/spl times/10/sup -5/ (1/MPa) at surface impurity concentration of 5/spl times/10/sup 19/ (cm/sup -3/) and it has enough sensitivity for mechanical sensor applications. The longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor increased up to 60% with a decrease in the cross sectional area, while transverse piezoresistance coefficient /spl pi//sub t[011]/ decreased with a increase in the aspect ratio of the cross section. These phenomena were briefly investigated based on a hole energy consideration and FEM (finite element method) stress analysis.

Analysis of piezoresistance in p-type silicon for mechanical sensors

Typical p-type silicon mechanical sensors are designed to operate under temperature range from /spl sim/173 K to /spl sim/373 K and subjected to stress less than /spl sim/100 MPa. The operation range is mainly restricted by the electrical and mechanical properties of silicon. The authors derived an approximate piezoresistance equation valid for typical operation range of the p-type silicon mechanical sensors, from valence band model of Bir and Pikus taking into account the spin-orbit interaction. The piezoresistance in p-type silicon was analyzed based on hole transfer and conduction mass shift due to stress. These mechanisms were introduced by Suzuki et al. [1984] to interpret piezoresistance in p-type silicon, based on the valence band equation in the vicinity of k=0. Under the typical operation range for p-type silicon mechanical sensors, holes are located where the value of k is relatively large, i.e., off k=0 and degenerate band split due to stress is incomplete. The hole behavior in the valence band was compatible with the typical operation range for p-type silicon mechanical sensors.

Fabrication of flexible thermopile generator

A thermoelectric power generation system is developed with a flexible structure. Its micro fabrication has the advantage of miniaturization and integration. Thermoelectric materials are fabricated by using micro fabrication technology. The developed structure is composed of a polyimide sheet as a substrate, thermoelectric materials deposited on the substrate, a heat absorber sheet and a heat sink sheet. The flexibility of this structure depends on the wavy form of the substrate and slits in the substrate, and the heat absorber and heat sink sheets. Because of the characteristic evaluation, open-circuit voltage of 16 µV K−1 per thermocouple was obtained. In addition, the thermopile generator does not break till a bending radius of curvature of 9 mm is reached. A prospect for practical application of the thermoelectric power generator for a curved surface was confirmed.

Piezoresistance measurement on single crystal silicon nanowires

A p-type single crystal silicon nanowire bridge and a four-terminal nanowire element were fabricated by electron-beam direct writing. The piezoresistance was investigated in order to demonstrate the usefulness of these sensing elements as mechanical sensors. The longitudinal piezoresistance coefficient πl[110] was found to be 38.7×10−11 Pa−1 at a surface impurity concentration of Ns=9×1019 cm−3 for the nanowire bridge. The shear piezoresistance coefficient π44 was found to be 77.4×10−11 Pa−1 at Ns=9×1019 cm−3 for the four-terminal nanowire element. These values are 54.8% larger than the values obtained from p+ diffused piezoresistors, which are used in conventional mechanical sensors.

Single crystal silicon piezoresistive nano-wire bridge

Air-bridge structure of p-type single crystal silicon nano-wire (NW) was fabricated by using 50 nm thick device layer and sacrificial layer etching of 130 nm thick buried oxide (BOX) in separation by implanted oxygen (SIMOX) substrate. The piezoresistance of the nano-wire bridge (NWB) was measured in order to verify its ability for sensing element of the nano-mechanical sensors. Longitudinal piezoresistance coefficient π 1[110] and apparent transverse piezoresistance coefficient π t[110] were found to be 38.7 x 10 -11 and 0 Pa -1 , respectively, at surface concentration of N s = 9 × 10 19 cm -3 . The value of π 1[110] was in close agreement with that of NW without releasing from the substrate, and 54.8% larger than that of p + diffused piezoresistor obtained by Tufte and Stelzer four decades ago (25 × 10 -11 Pa -1 and at N s = 9 × 10 19 cm -3 ). The value of apparent π t[110] was much smaller than that of the NW without releasing from the substrate. An advantage ofthe vanished apparent π t[110] for design of the piezoresistive mechanical sensors will be discussed. Obtained results are useful for design consideration of nano-metric piezoresistive elements used in the nano-mechanical sensors.

Design and fabrication of a miniaturized six-degree-of-freedom piezoresistive accelerometer

This paper presents a miniaturized six-degree-of-freedom (6-DOF) piezoresistive accelerometer. The accelerometer is capable of measuring three components of linear acceleration and three components of angular acceleration on three orthogonal axes at the frequency bandwidth of 300 Hz. The obtained experimental results showed good agreement with the finite element simulation. The sensor is ideal for use in biomechanical research applications requiring detection of multiple components of acceleration such as the study of human gesture recognition systems.

Analysis of piezoresistance in n-type β-SiC for high-temperature mechanical sensors

Piezoresistance in n-type β-SiC was analyzed on the basis of electron transfer and mobility shift mechanisms for cubic many-valley semiconductors. Gauge factors were calculated by using shear deformation potential constant Ⅺu. The calculation was compared with experimental results taken from the literature. It was shown that incorporation of the electron transfer and the mobility shift mechanisms gives reasonable interpretation for piezoresistance in n-type β-SiC within the temperature range from 300 to 673 K, and impurity concentration range from 1018 to 1020 cm−3. These conditions correspond to typical operation ranges of high-temperature piezoresistive sensors. The effect of the intervalley scattering on piezoresistance can be neglected from the evidence that gauge factor is inversely proportional to temperature within the abovementioned conditions.

Polymer based smart flexible thermopile for power generation

In this study, a flexible thermoelectric power generator has been proposed. The proposed thermoelectric power generator is composed of a Ni-Cu thermopile on a polymer sheet, and heat sink and heat absorber sheets. The flexible thermoelectric power generator has 60 mm-length, 45 mm-width and 3 mm-height. The flexible thermoelectric power generator may be possible to apply on a free form surface. As a result of characteristic evaluation, Seebeck voltage of 15.4 /spl mu/V/K per thermocouple was obtained, and a prospect for practical application was confirmed.

Thermoelectric micro power generator utilizing self-standing polysilicon-metal thermopile

A prototype self-standing polysilicon-metal junction thermopile has been developed. In order to realize ideal higher thermal isolation, a thermopile without a membrane and having self-standing structure is proposed. The hot and cold contacts in the proposed thermopile are reversible. The thermocouple is composed of an n-type polysilicon and an Au junction. The thermopile was fabricated by MICS (Micromachine Integrated Chip Service: three polysilicon layers structure) organized by the Cooperative Research Committee for Standardization of Micromachines in IEE of Japan. Output characteristics were measured as a function of distance between hot contact of the thermocouple and the radiation source, in order to confirm performance of the proposed thermopile as a micro power generator. Experimental results were in good agreement with the calculations.