Offset Temperature Coefficient Research Articles

A chip-level oven-controlled system used to improve accuracy of silicon piezoresistive pressure sensor

High precision is an important indicator for the silicon piezoresistive pressure sensor, which is deeply affected by the ambient temperature. This paper presented a chip-level oven-controlled system to operate the silicon piezoresistive pressure sensor at a constant temperature. However, the changes in ambient temperature still affect the temperature of the silicon piezoresistive pressure sensor due to the non-coplanar temperature control and the direct heat transfer between the piezoresistance on the surface of the pressure sensor and the environment. In order to decrease the effects and further improve the accuracy of the silicon piezoresistive sensor, a compensation function was introduced in the designed system. In addition, the oven-controlled structure fabricated by the MEMS process and the silicon piezoresistive pressure sensor were implemented at the chip level, which further reduced power consumption. The feasibility of the design was verified by the results of the thermodynamic model and COMSOL Multiphysics simulation analysis. Test results showed that when the pressure ranged from 100 hPa to 1100 hPa, the designed system performed a maximum measurement error no more than ±0.2 hPa from −45 °C to 45 °C. After compensation, the accuracy, sensitivity temperature coefficient, offset temperature coefficient of the silicon piezoresistive pressure sensor can reach 0.02% FS, 1.081 × 10−5/°C, 2.22 × 10−4% FS/°C respectively.

A 4 mm² Double Differential Torsional MEMS Accelerometer Based on a Double-Beam Configuration.

This paper reports the design and simulation of a 4 mm2 double differential torsional MEMS accelerometer based on a double-beam configuration. Based on the structure of conventional torsional accelerometers, normally composed of one pair of proof masses and one torsional beam, this work explores the double differential configuration: a torsional accelerometer with two pairs of unbalanced proof masses rotating in reverse. Also, the torsional beam is designed as a double-beam structure, which is a symmetrical structure formed by two torsional beams separated by a certain distance. The device area of the novel accelerometer is more than 50 times smaller than that of a traditional double differential torsional MEMS accelerometer. The FEM simulation results demonstrate that the smaller device does not sacrifice other specifications, such as mechanical sensitivity, nonlinearity and temperature robustness. The mechanical sensitivity and nonlinearity of a ±15 g measuring range is 59.4 fF/g and 0.88%, respectively. Compared with traditional single-beam silicon structures, the novel structure can achieve lower maximum principle stress in critical regions and reduce the possibility of failure when high-g acceleration loading is applied along all three axes. The mechanical noise equivalent acceleration is about in the theoretical calculations and the offset temperature coefficient is 0.25 mg/ in the full temperature range of to .

A double differential torsional micro-accelerometer based on V-shape beam

This paper reports the design, simulation, fabrication and measurement of a double differential torsional micro-accelerometer based on V-shape beam. The structure of conventional torsional micro-accelerometers is typically composed of two unbalanced proof masses and a torsional beam. This work develops a torsional micro-accelerometer with an optimized structure, which is composed of four proof masses splitting into two pairs. The two pairs of unbalanced masses have the opposite sensitivity to acceleration but the same sensitivity to off-acceleration input, and by using double differential arithmetic the sensitivity, environment robustness and bias stability can be improved. The accelerometer prototype is fabricated with the pre-buried mask wet-etching method and tested. The resonant frequency and quality factor are about 1485Hz and 28.02 respectively. The sensitivity and nonlinearity of the measuring range ±15g is 0.14mV/g and 0.22% respectively. The x-axis and y-axis cross-axis errors are 0.04% and 0.69% respectively. The 1g bias stability of the accelerometer is 0.11mg for 1h and the Allan deviation is 8.7μg. In the full temperature range of −40°C to +60°C,the temperature sensitivity of the scale factor is 49.9ppm/°C while the offset temperature coefficient is 0.22mg/°C after temperature compensation.

Capacitive pressure sensor with monolithically integrated CMOS readout circuit for high temperature applications

An integrated capacitive surface micromachined pressure sensor for high temperature applications was developed and characterized to work at temperatures up to 250 °C. The sensor and the CMOS readout circuit are processed on separation by implantation of oxygen (SIMOX) substrates. The readout circuit is programmable and allows calibration of linearity, offset and output range. The performance of a 20 and 50 bar sensor is discussed. Even without active temperature compensation the offset temperature coefficient (TCO) referred to full scale output (FSO) is less than 0.03%/°C between 25 and 150 °C and less than 0.09%/°C between 150 and 250 °C. The compensated linearity error is less than 0.4% FSO.

CMOS-compatible capacitive high temperature pressure sensors

A new surface-micromachined capacitive single chip pressure sensor for high temperature applications using separation by implantation of oxygen (SIMOX) substrates is presented. The production steps are CMOS-compatible and allow on-chip integration of high temperature readout electronics. Measurements have been performed in a temperature range from 50°C to 340°C. Three different types of sensors have been investigated with a pressure range of 38, 85 and 125 bar. In the temperature range from 50°C to 250°C, the offset temperature coefficient (TCO) of the sensors is below the measurable accuracy. In the temperature range from 250°C to 340°C, the TCO falls off to −5000 ppm/°C due to induced stress of the package. Sensors that are released from the package show a maximum TCO of less than 500 ppm/°C over the whole temperature range.

An integrated force-balanced capacitive accelerometer for low- g applications

A low-cost monolithic accelerometer which incorporates a surface-micromachined polysilicon sensor with bipolar/MOS interface circuitry on a single chip has been developed for a measurement range of ± 5 g. The accelerometer has a noise floor of 0.6 m g (Hz) 1 2 and a shock survival rating of 1000 g. A sensitivity temperature coefficient ± 50 ppm °C −1 and an offset temperature coefficient of ±5 m g °C −1 have been achieved over the −40 to +105 °C automotive temperature range. A wide bandwidth from d.c. to 4 kHz is adjustable using a single external capacitor. The accelerometer operates on a single 5 V power supply and consumes 40 mW of power. It provides an analog output of 200 mV g −1 and a digitally activated self-test output of −5 g.

High-precision readout circuit for LIGA acceleration sensors

Abstract For the past few years capacitive LIGA acceleration sensors have been fabricated at the Karlsruhe Nuclear Research Center. The advantages of LIGA acceleration sensors are their high zero-acceleration capacitance of 5 pF, temperature-compensated design with low offset temperature coefficient (TCO = 1.5 × 10−4 FSO K−1) and high linearity. In addition, a high-precision readout circuit has been developed. The electronic circuit's distinguishing feature is its extremely low noise, so that capacitance changes of 5 aF Hz −1 2 can be detected. Combined with a 1g LIGA acceleration sensor, a resolution of 1μg Hz −1 2 has been achieved. A feedback system has been developed for a further improvement of linearity. The electronic circuit has been realized as a multichip module (MCM) in multilayer thick-film technique on a 10 mm × 20 mm Al2O3 substrate. The final result is a sensor system with excellent properties as regards temperature behaviour, dynamic range and resolution.

Highly stable solid-state x-ray detector array.

A detailed analysis of the effects of temperature changes, over time and between array elements, on the generation of circular artifacts in images produced by x-ray computed tomography was reported. We give formulas for calculating--according to the x-ray energy, detector sensitivity, and observed image quality (contrast and spatial resolution)--the maximum offset temperature coefficient and maximum gain temperature coefficient that will allow circular-artifact-free imaging. A temperature-controlled and insulated solid-state x-ray detector array, consisting of Gd2O2S:Pr,Ce,F ceramic scintillators coupled to crystal Si pin-photodiodes and designed to meet the requirements for these coefficients, produced high-resolution artifacts-free CT images of a phantom head.

An Ultra-Low Drift Amplifier Using a New Type of Series-Shunt MOSFET Chopper

A chopper amplifier of a new type is proposed for the amplification of nanovolt-order dc voltage. The chopper is built by connecting a shunt switch, which is driven at twice the chopper frequency, to the output terminals of a conventional and balanced-type series-shunt MOSFET chopper. The present chopper is free from offset voltage arising from spike voltages and has an input voltage offset temperature coefficient of less than 0.1 nV/°C for a signal source of less than 1 k?, and a long-term drift of 2 nV/18 h for signal source resistance of 6.1 ?.

An offset temperature coefficient in SQUID sensors

Output offsets in SQUID sensors which accompany changes in the sensor temperature have been measured under varying conditions of magnetic stress applied to the sensor films. It is shown that there is an offset temperature coefficient (OTC), characterizing a reversible variation of the offset with temperature, which depends upon magnetic stress. Further, the variations of the OTC with magnetic stress are shown to be reversible for stress values below a critical value. Above this critical value, an irreversible change in the OTC occurs. This change can be annealed out by heating the sensor above its critical temperature. Two mechanisms which are capable of producing an OTC which behaves in this manner are discussed in quantitative terms. One mechanism involves temperature dependent pinning forces and the other involves the temperature dependent shielding currents which flow in response to magnetic stress. A simple technique for minimizing the deleterious effects of the OTC on magnetic measurements is described.