Kazuji Yamada

Nonlinearity of the piezoresistance effect of p-type silicon diffused layers

The nonlinearity of the piezoresistance effect of p-type layers diffused into the{110}silicon plane has been investigated. An expression which contains higher order stress terms and can treat the piezoresistance effect quantitatively has been derived. It has been found that third-order stress terms are sufficient to give a good approximation of the effect. The expression coefficients have been determined experimentally using a silicon cantilever on which p-type diffused layers having surface concentration values from 1018to 1019cm-3are formed. Nonlinearity in the case where the longitudinal axis of the cantilever is perpendicular to the direction of current flow is greater than that in the case where it is parallel to the direction of current flow under both tensile and compressive stresses. Using the new expression, it has been confirmed that results of numerical analysis on the nonlinearity of trial silicon piezoresistive pressure sensors agree well with experimental results.

A piezoresistive integrated pressure sensor

Abstract A silicon piezoresistive integrated pressure sensor (IPS) containing sensing, temperature compensation and amplification circuits has been developed for automotive and industrial applications, etc. The chip of the IPS is bonded on a silicon support 2 mm thick, using an electrostatic bonding technique for reducing unwanted thermal stress from the support and package. Temperature invariant and laser trimmable printed thick film resistors for adjusting temperature compensation and Transfer function scaling are formed on the ceramic plate around the IPS chip, which is then mounted in a modified TO-3 package as a three terminal device. Experimental results and simulations of span temperature compensation in the sensing element bridge and the fully assembled IPS are shown here to be in good agreement. The temperature dependence of the zero and non-linearity of the IPS are also described.

Ag-Pd thick film conductor for AlN ceramics

An Ag-Pd thick-film conductor for aluminum nitride (AlN) ceramics was developed. The conductor showed adhesion strength and reliability almost comparable to those of commercial conductors for alumina ceramics. The influence of physical properties of the lead oxide glass frit on conductor performance was studied, and the most suitable glass was selected for the frit material. The softening point of frit glass has the largest effect on conductor performance; this temperature should be approximately 500 degrees C. If the softening point was either too high or too low, compared to the sintering temperature of the conducting metals, poor adhesion strength resulted. Use of glass with too high a softening point caused poor wettability but resistance to erosion by Pb-Sn solder, while it resulted in good wettability but poor erosion resistance when the softening point was too low. Additionally, Cr-, Ti, and Zr-oxides were identified as wettability-promoting agents. The molten glass did not penetrate into the AlN ceramics; rather, it remained on the surface. This behavior differed from that in the case of alumina ceramics, for which the molten glass penetrated along the grain boundaries. >

The influence of moisture on surface properties and insulation characteristics of AlN substrates

The influence of moisture on the surface properties and insulation characteristics of sintered aluminum nitride (AlN) substrates was investigated. Two AlN substrates, one nontreated and the other with an oxidizing heat treatment, were exposed to moisture under several sets of conditions. For the nontreated substrate, changes in weight and surface properties were not observed, and neither was degradation of insulation characteristics under high temperature and humidity test conditions (80 degrees C, 90% RH). Under more severe conditions of a pressure cooker test (121 degrees C, 2 atm, water vapor), the surface morphology changed and the insulation characteristics were degraded. These changes are attributed to formation of a new surface layer on the substrate. Verification of this hypothesis was undertaken by carrying out an immersion test in warm water (80 degrees C). Clear changes in surface morphology were seen. Meanwhile, the oxidized substrates were found to experience no changes in weight or surface morphology under the pressure cooker test. It is concluded that the thermal oxidation process is an effective way to protect the AlN substrates against moisture and the subsequent degradation of the insulation characteristics. >

Differential Pressure/Pressure Transmitters Applied with Semiconductor Sensors

The optimum design for silicon diaphragm-type pressure sensors and that for a sensing body of the transmitters have been considered. Three types of sensors, which have different section shapes, have been developed for measuring wide-range pressure with high sensitivity and good linearity. The transmitters of the range from 0-100 Pa up to 0-50 MPa with an accuracy of 0.2 percent have been developed. For a differential pressure transmitter a three-metal diaphragm structure has been devised to protect the sensor from an overpressure. The characteristics of the transmitters are high accuracy, high reliability, and long-term stability.

Characteristic analysis of a pressure sensor using the silicon piezoresistance effect for high-pressure measurements

The characteristics of output voltages and non-linearities of a silicon circular diaphragm pressure sensor using the piezoresistance effect are analysed for high-pressure measurements. The pressure sensor is analysed, using triaxial stresses and their corresponding piezoresistance coefficients, by a finite-element method (FEM). Radial and tangential stresses on the circular diaphragm, calculated by the FEM at a pressure of 50 MPa, shift by about 125 MPa to the compressive side from those calculated by plate theory of a fixed periphery. Moreover, the perpendicular stress (z stress) component to the diaphragm surface is not negligible at high pressure in either calculation. The results calculated by the FEM agree well with the experimental results. A pressure sensor for high-pressure measurements from 0 to 50 MPa is then designed and fabricated. It has a non-linearity within +or-0.1%.

Low-pressure measurement limits for silicon piezoresistive circular diaphragm sensors

The lower limit to a practical measurable span is investigated for pressure sensors that have a silicon diaphragm with circular shape and employ piezoresistive gages. Output voltages and non-linearities of the sensors are analysed, taking into account the effects of the diaphragms large deflection and the piezoresistive effect non-linearities. Based on this analysis and industrial requirements (the minimum span output voltage must be larger than 4.3 mV V-1 and non-linearities must be within +or-0.2% at the same time), it is found that the minimum span is 15 kPa.

2000 V 500 A high power IGBT module

A high voltage and a large current rating, 2000 V 500 A IGBT (Insulated Gate Bipolar Transistor) module with a newly developed structure was described. The module features a small size, high reliability and low electrical noise characteristics. The high reliability is realized by using a low thermal expansion base. The modules are suitable for applications to high speed switching levels with high blocking voltages such as in traction motor drives.

A CPU chip-on-board module

A CPU chip-on-board module for low and midrange computers is described. The module consists of a CPU bare chip, 24 SRAMs packaged in SOJ packages, and some decoupling capacitors. The module substrate is a printed circuit board (PCB) made of bismaleimide-triazine resin. The module (156 mm/spl times/58 mm) consists of four signal metal layers and four power/ground metal layers. A square clearance hole (17 mm/spl times/17 mm) for the CPU is formed in the central part of the PCB. A thermal spreading metal is glued to the PCB from the rear side, covering the square hole, and the CPU chip is die-bonded onto the metal plate. The thermal resistance can be made smaller than 2/spl deg/C/W with 0.4 m/s of wind velocity. Numerical analysis of electrical characteristics of the module shows that it can reduce signal delay time from the CPU to cache memories by 10% compared with that of a daughter board type module with the CPU packaged in a pin-grid array package. It is estimated that simultaneously switched noise can be reduced by 60% from that of the daughter board type module. >

Thick film resistors for AlN ceramics

RuO/sub 2/ thick-film resistors for aluminum nitride (AlN) ceramics with controlled temperature coefficient of the resistor (TCR) and reliabilities have been developed. The resistors, in the range of approximately 10 Omega / Square Operator to 10 k Omega / Square Operator were obtained using a crystallized glass powder and a RuO/sub 2/ powder, binder materials, and a conducting material. The glass had a low PbO content of 6 wt %, a low thermal expansion coefficient of 3.6*10/sup -6// degrees C, and a softening point of 610 degrees C. The resistors, to which MnO/sub 2/ was added to the above combination, had excellent TCRs of +or-250 p.p.m./ degrees C at 30 Omega / Square Operator to 30 k Omega / Square Operator . These resistors showed small resistance changes, which were less than +1.0% after a thermal cycle test (-55-150 degrees C, 1000 times) and high-temperature storage test, ( 150 degrees C, 1000 h). They had excellent resistance stability. Further, the effect of particle size of glass and RuO/sub 2/ powders on electrical properties of the resistors containing the crystallized glass was similar to that in resistors containing noncrystallized glass for alumina ceramics. >