Showing papers on "Gauge factor published in 1998"

Stress-dependent hole effective masses and piezoresistive properties of p -type monocrystalline and polycrystalline silicon

Abstract: Piezoresistive effects of $p$-type polycrystalline silicon underline that longitudinal and transversal piezoresistive properties in monocrystalline silicon do not have the same physical origin, which is not accounted for in current models. This difference is highlighted by the study of the mechanical stress effect on the valence band, which shows that piezoresistive properties of $p$-type monocrystalline silicon can be explained in terms of both hole transfer between heavy- and light-hole valence bands and stress-dependent hole effective masses. The quantification of these phenomena points out that longitudinal piezoresistive properties are mainly due to the hole transfer, whereas transversal ones are mainly attributed to the effective mass change effects. This enables one to model $p$-type polycrystalline silicon piezoresistivity, in particular the sign change of the transversal gauge factor at high doping level.

Ultra-high sensitivity intra-grain poly-diamond piezoresistors

Abstract: Chemical vapor deposited (CVD) polycrystalline diamond is inexpensive and can become a commercially viable piezoresistive sensor material if its typical gauge factor (GF) exceeds that of crystalline Si and SiC. In this paper, a study of GF of B-doped polycrystalline diamond film leads to an intra-grain GF above 4000, which is comparable to GF of single crystal p-type diamond. This result, reported for the first time, shows that large-grain (50–80 μm) CVD diamond can be used to build inexpensive ultra-high sensitivity piezoresistive sensors.

High sensitivity spin-valve strain sensor

Abstract: A technique for detecting strain has been demonstrated based on a spin-valve sensor. The 400 A thick sensor has been integrated onto an atomic force microscope cantilever. An applied strain caused by bending of the cantilever changes the orientation of the free-layer magnetization due to magnetostriction. This in turn results in a change in the electrical resistance because of the giant magnetoresistance effect. With the proper magnetic bias, a base-line strain sensitivity of 10−10/Hz1/2 has been achieved. The corresponding gauge factor of 150 is roughly 1.6× that of similar silicon piezoresistive cantilevers. In the future, one might be able to enhance the sensitivity by another factor of 3–5.

Review on diamond based piezoresistive sensors

Abstract: Nearterm industrial applications require pressure sensors and acceleration sensors which are able to operate at elevated temperatures and in harsh environments where conventional silicon devices do not work. Many properties of diamond (e.g. its physical hardness, high Young's modulus, high tensile yield strength, chemical inertness, low coefficient of friction and high thermal conductivity) make diamond an excellent material for micromechanical device applications which include piezoresistive (e.g. pressure and acceleration) sensors. The measurement of the gauge factor of B-doped, polycrystalline CVD diamond thin films leads to the result that the longitudinal piezoresistive effect is larger than the transverse piezoresistive effect for all B-doping concentrations. Furthermore, the transverse piezoresistive effect shows a pronounced nonlinearity. Therefore, a "longitudinal" pressure sensor lay out should be preferred. In general, the longitudinal gauge factor increases with decreasing doping concentration and can be larger than 100, which is comparable to single-crystalline silicon, and larger than the reported gauge factors of SiC. First prototype pressure sensors with B-doped polycrystalline diamond piezoresistors connected to form a Wheatstone bridge on top of a silicon square membrane (1300 /spl mu/m/spl times/1300 /spl mu/m/spl times/30 /spl mu/m) show an excellent linearity. The sensitivity of 1.64/spl times/10/sup -5/ mV/(V Pa)/sup -1/ can be improved using a lower doping concentration of the piezoresistors.

Preparation and Piezoresistive Properties of Polycrystalline SnO2 Films

Abstract: Tin oxide thin films were deposited by dc magnetron sputtering in a gas mixture of Ar and O2 using a target containing antimony. The films were characterized using X-ray diffraction. The films showed preferred orientation in a or plane. The properties of films depended on the substrate temperature and the gas flow ratio of Ar/O2. The piezoresistive properties of these films have been measured using a conventional cantilever method. The gauge factor was measured to be around negative 5–20 at room temperature, which is comparable to the gauge factor of polycrystalline silicon films.

Comparison of bulk- and surface-micromachined pressure sensors

Abstract: Two piezoresistive micromachined pressure sensors were compared: a commercially available bulk-micromachined (BM) pressure sensor and an experimental surface-micromachined (SM) pressure sensor. While the SM parts had significantly smaller die sizes, they were outperformed in most areas by the BM parts. This was due primarily to the smaller piezoresistive gauge factor in the polysilicon piezoresistors in the SM parts compared to the single crystal strain gauge used in the BM parts.

Sensitive Strain Gauge Using a CMOS IC Combined with an Amorphous Magnetostrictive Wire Cantilever Beam

Abstract: A highly sensitive linear strain gauge using a pair of amorphous CoSiB wires fixed to a plastic cantilever beam combined with a CMOS IC multivibrator circuit is presented. The wires are magnetized with a sharp pulse current to generate the stress impedance (SI) effect, showing a gauge factor of about 2000 in the CMOS IC circuit The linear strain gauge shows a resolution of about 2.5 mg for weight detection with high linearity in the range of −0.75∼1.25 g. The mechanism of the SI characteristics in the CoSiB wire is analyzed using a magnetization rotation model. Pulsation of fingertip blood vessels was stably detected by using the SI gauge stress sensor.

Practical model for electrical properties of highly doped p-type polysilicon

Abstract: This paper describes a new approach to practical modelling of electrical properties of polycrystalline semiconductors. The model combines the electro-physical properties of microcrystalline silicon films with that of monocrystalline silicon so that the former properties are attributed to the grain boundaries regions and the latter to intragrain regions. The model is used to describe the dependence of resistivity (/spl rho/), its temperature coefficient (TC/spl rho/) and gauge factor (G) of highly boron doped polycrystalline silicon, 4.10/sup 25/ to 10/sup 27/ m/sup -3/, on the dopant concentration for different grain sizes, 10/sup -8/ to 10/sup -6/ m. It is shown that at the high doping level /spl rho/ (TC/spl rho/) of polysilicon is higher (lower) than that of monosilicon, being dependent on the average grain size. The gauge factor of polysilicon is lower than that of monosilicon not only because of the "random" orientation of the grains but also because of lower values of gauge factor at the grain boundaries. For lower doping concentration (smaller grain sizes) the TC/spl rho/ of polysilicon becomes negative revealing the higher contribution of grain boundaries.

Diamond microelectromechanical sensors (DMEMS)

Abstract: CVD deposited diamond films, processed similar to conventional semiconductor devices, are used to achieve microelectromechanical systems (MEMS). Cantilever beams, membranes, stripes, and tips used as components in accelerometers, pressure sensors, and other devices can be constructed in doped and undoped diamond films. This paper will focus on the aspects of achieving diamond MEMS (DMEMS) for a high bandwidth, high temperature pressure sensor. The high elastic modulus of diamond provides a stiff substrate for the high temperature electromechanical device. The intended operating range of the device is over 600/spl deg/C, measuring dynamic pressures with a 0.002 psi response. The effects of temperature on ionization of dopants, the piezoresistance and gage factor of diamond are measured. The diamond pressure sensor has two key components, the intrinsic diamond membrane and the doped diamond piezoresistors (PZRs). These piezoresistors are delineated by an etch process and reside integral to the i-diamond membrane and substrate. Processing and behavior results of such diamond microstructures will be discussed. Also, PZR element placement on the membrane is evaluated for strain effect, signal, and gauge factor performance. The effect of the conductivity of i-diamond on sensor behavior, particularly at higher temperatures is evaluated. Further, the mechanical strength of the diamond membranes is examined.

Theoretical design of calibration beams for strain gauge factor measuring apparatus

Abstract: By starting with theoretical analysis and combining with the needs of practical applications, this article carries out a preliminary theoretical investigation of optimum design of the cross sectional shape and dimensions of calibration beams for strain gauge factor measuring apparatus. A new formula is derived in this paper that shows the quantitative relationship among strains on the beam surfaces, the strain non-uniformity within a certain range of the beam and beam thickness, which provides a theoretical basis for the accuracy improvement of the measuring apparatus and for correct application of the calibration beams, and also for drawing up and improving items concerning with calibration beams in strain gauge standards internationally. It is proven through experiments that the neutral axis of the bent calibration beam of rectangular cross section under pure bending moments is actually not circular but parabolic.