Silicon Piezoresistive Pressure Research Articles

Low-Cost Sensor for Continuous Measurement of Brix in Liquids

This paper presents a Brix sensor based on the differential pressure measurement principle. Two piezoresistive silicon pressure sensors were applied to measure the specific gravity of the liquid, which was used to calculate the Brix level. The pressure sensors were mounted inside custom-built water-tight housings connected together by fixed length metallic tubes containing the power and signal cables. Two designs of the sensor were prepared; one for the basic laboratory testing and validation of the proposed system and the other for a fermentation experiment. For lab tests, a sugar solution with different Brix levels was used and readings from the proposed sensor were compared with a commercially available hydrometer called Tilt. During the fermentation experiments, fermentation was carried out in a 1000 L tank over 7 days and data was recorded and analysed. In the lab experiments, a good linear relationship between the sugar content and the corresponding Brix levels was observed. In the fermentation experiment, the sensor performed as expected but some problems such as residue build up were encountered. Overall, the proposed sensing solution carries a great potential for continuous monitoring of the Brix level in liquids. Due to the usage of low-cost pressure sensors and the interface electronics, the cost of the system is considered suitable for large scale deployment at wineries or juice processing industries.

A package for piezoresistive pressure sensors with embedded built-in self-test function based on bimetallic actuator

Piezoresistive pressure sensors have been widely used in the industry and many other fields. However, conventional pressure sensor inspection is performed with the device off, which causes several inconveniences. In this article, an electrothermal actuator is designed and fabricated on the basis of bimetallic alloy material to realise the self-test of the piezoresistive silicon pressure sensor, and a kind of pressure sensor package structure with self-test capability is developed using the electrothermal actuator. Experimental results show that the structure can realise the dual excitation of the pressure and temperature of the diffused silicon pressure sensor core and enable it to return to the normal working state in less than 3.3 s. The self-test module can be driven at a low voltage of 0.8 V at less than 618 mW and can reflect the performance of the pressure sensor quickly and accurately. The structure is suitable for most differential pressure, absolute pressure sensor chips.

Monitoring and Analysis of Pore and Earth Pressure at the Pile Surface Using Piezoresistive Silicon Pressure Transducers

The piezoresistive silicon pressure transducers based on the piezoresistive effect have demonstrated their potential in the accurate monitoring of pressure. However, their usage in the pore and earth pressure monitoring at the pile surface under hydraulic jacking has not yet been explored. In this study, two self-made model piles (one is a closed-ended pile and the other is an open-ended pile) were instrumented with piezoresistive silicon earth transducers and pore pressure transducers and then driven into the soil using a hydraulic jack. A comprehensive investigation was first carried out for the structure of the model piles, the installation procedure of the transducers, and the composition of the test system. The pore and earth pressure measurements of the transducers were used for the evaluation of the distribution of the pore pressure, excess pore pressure, radial earth pressure, and radial effective earth pressure. The model test results indicate that the piezoresistive silicon pressure transducers are suitable for monitoring the pore and earth pressure at the pile surface during jacking. In addition, the pore pressure, excess pore pressure, radial earth pressure, and effective radial earth pressure along the test piles were affected by the penetration depth and the pile end form.

Relative Contributions of Packaging Elements to the Thermal Hysteresis of a MEMS Pressure Sensor

Piezoresistive silicon pressure sensor samples were thermally cycled after being consecutively packaged to three different levels. These started with the absolute minimum to allow measurement of the output and with each subsequent level incorporating additional packaging elements within the build. Fitting the data to a mathematical function was necessary both to correct for any testing uncertainties within the pressure and temperature controllers, and to enable the identification and quantification of any hysteresis. Without being subjected to any previous thermal preconditioning, the sensors were characterized over three different temperature ranges and for multiple cycles, in order to determine the relative contributions of each packaging level toward thermal hysteresis. After reaching a stabilised hysteretic behaviour, 88.5% of the thermal hysteresis was determined to be related to the bond pads and wire bonds, which is likely to be due to the large thermal mismatch between the silicon and bond pad metallisation. The fluid-fill and isolation membrane contributed just 7.2% of the total hysteresis and the remaining 4.3% was related to the adhesive used for attachment of the sensing element to the housing. This novel sequential packaging evaluation methodology is independent of sensor design and is useful in identifying those packaging elements contributing the most to hysteresis.

Evaluation and Signal Conditioning of Piezoresistive Silicon Pressure Sensor

The piezoresistive silicon pressure sensor used in this work is developed by Technical University Berlin. It is mainly composed of a silicon-membrane and four implanted piezoresistors connected in form of a Wheatstone bridge. After wire bonding, the sensor was evaluated in a climate cabinet at different temperatures and pressures. The characteristic curve of the sensor shows its good linearity and strong dependence on the temperature. The sensor ́s temperature coefficient of sensitivity and zero shift were compensated using ASIC MLX90308. The experimental results show that this method of compensation accurately solved the sensors temperature dependence problems.

High temperature fast response pressure probe for use in liquid metal droplet dispensers

A miniature fast response high temperature pressure probe, with demonstrated use in liquid metals up to 255 °C (528 K), has been developed. Innovative packaging technologies have been applied to integrate a conventional piezoresistive silicon pressure sensor into the probe, without the need of an auxiliary water-cooling system. In situ static calibrations are used to verify the linearity of the pressure signal and the stability of the pressure sensitivity (0.5% standard deviation over 70 min at 255 °C). Dynamic calibration, completed in an air shock tube facility, yields the probe's natural frequency. This frequency, when corrected for probe operation in liquid tin, is found to be 100 kHz. The reliability and accuracy of the probe is assessed by mounting it in a tin droplet dispenser for use in an extreme ultraviolet light source. Droplet dispensers typically include an excitation mechanism, which can be based on the generation of acoustic pressure waves to impose a desired droplet frequency. The probe accuracy is verified by the comparison of pressure measurements with laser Doppler vibrometry measurements of the pressure generating structure. A reference pressure measurement, conducted at representative conditions, shows a complex frequency response, with peaks distributed over three orders of magnitude and maximum amplitude of 440 mbar. Time variance of the excitation mechanism due to thermal transients is studied by monitoring the pressure response during operation. Finally, the linearity of the excitation system, with respect to the excitation amplitude, is verified by response measurements. In conclusion, the developed probe is capable of characterizing the excitation mechanism of a liquid metal droplet dispenser. Additionally, real-time monitoring of the performance of the excitation system during long-term operation is possible.

Fluctuating wall pressures measured beneath a supersonic turbulent boundary layer

Wind tunnel experiments up to Mach 3 have provided fluctuating wall-pressure spectra beneath a supersonic turbulent boundary layer to frequencies reaching 400 kHz by combining data from piezoresistive silicon pressure transducers effective at low- and mid-range frequencies and piezoelectric quartz sensors to detect high frequency events. Data were corrected for spatial attenuation at high frequencies and for wind-tunnel noise and vibration at low frequencies. The resulting power spectra revealed the ω−1 dependence for fluctuations within the logarithmic region of the boundary layer but are essentially flat at low frequency and do not exhibit the theorized ω2 dependence. When normalized by outer flow variables, a slight dependence upon the Reynolds number is detected, but Mach number is the dominant parameter. Normalization by inner flow variables is largely successful for the ω−1 region but does not apply for lower frequencies. A comparison of the pressure fluctuation intensities with 50 years of historical data shows their reported magnitude chiefly is a function of the frequency response of the sensors. The present corrected data yield results in excess of the bulk of the historical data, but uncorrected data are consistent with lower magnitudes, suggesting that much of the historical compressible database may be biased low.

Attachment of MEM piezoresistive silicon pressure sensor dies using different adhesives

This paper gives comparison and discussion of adhesives used for attachment of silicon piezoresistive pressure sensor dies. Special attention is paid on low pressure sensor dies because of their extreme sensitivity on stresses, which can arise from packaging procedure and applied materials. Commercially available adhesives ?Scotch Weld 2214 Hi-Temp? from ?3M Co.? and ?DM2700P/H848? from ?DIEMAT?, USA, were compared. First of them is aluminum filled epoxy adhesive and second is low melting temperature (LMT) glass paste. Comparing test results for low pressure sensor chips we found that LMT glass (glass frit) is better adhesive for this application. Applying LMT glass paste minimizes internal stresses caused by disagreement of coefficients of thermal expansions between sensor die and housing material. Also, it minimizes stresses introduced during applying external loads in the process of pressure measuring. Regarding the measurements, for the sensors installed with filled epoxy paste, resistor for compensation of temperature offset change had negative values in all cases, which means that linear temperature compensation, of sensors installed this way, would be impossible. In the sensors installed with LMT glass paste, all results, without exception, were in their common limits (values), which give the possibility of passive temperature compensation. Furthermore, LMT glass attachment can broaden temperature operating range of MEM silicon pressure sensors towards higher values, up to 120 ?C.

Meteorological rocket sonde of meridian project and its detection results

摘要: 研发了一种采用GPS体制的气象火箭探空仪, 此种探空仪采用超小快速响应型珠状负温度系数热敏电阻温度传感器、压阻式硅气压传感器和GPS接收机. 与其他类型的气象火箭探空仪相比, 具有温度、气压、密度、风场等气象要素测量准确度高, 遥测接收设备简单便携, 发射前的准备工作简单, 系统可靠性高等优势, 并在子午工程发射试验中实现成功测试. 关键词: 子午工程 / 气象火箭探空仪 / 传感器 / GPS接收机

Flip-chip packaging of piezoresistive pressure sensors

A packaging technology for piezoresistive silicon pressure sensors is presented which is based on the use of standard flip-chip bonding of the sensor die on a printed circuit board. The assessment of the packaging proposal has been carried out by using low-range, high-sensitivity relative pressure sensors. The characterization of the fabricated devices has shown the feasibility of the proposal in terms of stability and sensitivity although a higher dependence of the sensitivity on temperature than in the case of standard packaging. Since this drawback can readily be compensated for by the signal conditioning circuitry, the proposed packaging scheme can be of interest for cost-limited applications.

A study on the thermal behavior of fabrication processes for micro-accelerometer by SOI wafers

The remarkable progress in technology of micro-machining fabrications over the past 30 years has promoted the development of many types of silicon micro-sensors. Mercerization of sensor is a trend of the silicon sensor development with regard to a piezo resistive silicon pressure sensor, the size of the pressure sensor diaphragm have become smaller year by year, and a micro-accelerometer with a size less than 200–300 μm has been realized. Over the past 4 or 5 years, numerical modeling of micro-sensors and micro-structures has gradually been developed as a field of micro-electro-mechanical system (MEMS) design process. In this paper, we study some of the micro-machining processes of single crystal silicon (SCS) for the micro-accelerometer, and their subsequent processes, which might affect thermal and mechanical loads. The finite element method (FEM) has been a standard numerical modeling technique extensively utilized in structural engineering discipline for component design of micro-accelerometer. Temperature rises sufficiently low at the suspended beams. Instead, larger temperature gradient can be seen at the bottom of paddle part. The center of paddle part becomes about 5–20 °C higher than the corner of paddle and suspended beam edges.

Calibration and temperature compensation of silicon pressure sensors using ion-implanted trimming resistors

A piezoresistive silicon pressure sensor with bipolar on-chip signal conditioning circuits permits offset voltage, full scale span and temperature coefficient of offset voltage and full scale span to be calibrated from a trimming ion-implanted resistors. The ion-implanted resistors with temperature coefficient of 1700 ppm/°C or 4700 ppm/°C were fabricated by the same process as that used for the base and piezoresistors. The fabricated sensor exhibits a sensitivity of 40.5 mV/kPa and temperature coefficient of 46 ppm/°C at the temperature range of −10 to 70°C.

Photolithographic packaging of silicon pressure sensors

The packaging technique presented here provides direct interaction between the sensing element and the physical or chemical variable to be measured as well as hermetic insulation and mechanical protection of the silicon sensor and its electrically active components. The sensors are embedded in a mechanically decoupling shell of silicone elastomer with low Young's modulus, leaving the sensing area free from covering. The process can be considered as a synthesis of conventional soft-mounting techniques and photolithographically controlled partial encapsulation. It has been applied to package piezoresistive silicon pressure sensors for use in humid environments and the results obtained show the suitability of the concept. Due to its modularity and unlike application-specific packaging methods, it can potentially be applied to a variety of microelectronic sensors.

Electronically scanned multichannel pressure transducer system for cryogenic environments

Research into the application of custom doped piezoresistive silicon pressure sensors has led to a multichannel pressure sensor design that will operate accurately and reliably at cryogenic temperatures. The thermal effects upon multichannel pressure sensors are mapped by thermal calibrations and are represented by sets of nth order coefficients specific to each sensor. The thermal offset and sensitivity variations are corrected by computer algorithms which scan the sensors, recall correction coefficients from thermally induced sensor variations and apply these to correct the sensor's output measurement uncertainty to within 0.5% of full scale output for combined offset and sensitivity. A prototype sensor system has been fabricated and performance test data are presented.

Thermal noise in piezoresistive silicon microphones

Recent developments in micromachining of silicon devices and piezoresistive silicon pressure sensors have led to the consideration of the limitations of silicon pressure sensors as a microphone. Fundamental and technological limits to device scaling are presented, which provide design criteria for sensitivity and pressure accuracy, along with dynamic range and bandwidth. An analysis on the nature of noise and fundamental noise mechanisms is presented to determine the theoretically achievable input resolution. Primary noise considerations are given with regard to thermal noise and shot effects. Performance variation of the sensor in both offset voltage and sensitivity is discussed as a function of temperature and impurity density of a standard bridge configuration. Finally, models of the various noise mechanisms are proposed.

An interchangeable silicon pressure sensor with on-chip compensation circuitry

A new concept for the calibration and temperature compensation of a piezoresistive silicon pressure sensor is proposed, in which the piezoresistive Wheatstone bridge is combined on chip with a trimmable polysilicon resistor network. The design, fabrication and measured characteristic of a sensor based on this concept are presented.

A theoretical study of transducer noise in piezoresistive and capacitive silicon pressure sensors

An analysis of the effect of noise introduced by the transduction process on the minimum detectable signal (MDS) of piezoresistive and capacitive pressure sensors has been performed. MDS is first introduced as an appropriate figure of merit for comparing different sensor transduction schemes. Analyses are then performed to determine the minimum MDS theoretically achievable for a broad range of generic transducer circuits. The results of the analyses indicate that noise in the transduction process is not a limiting factor in the performance of properly designed integrated silicon sensors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

SENSIM: A simulation program for solid-state pressure sensors

A simulation program is described which is capable of calculating the output response of silicon piezoresistive or capacitive pressure sensors as a function of both pressure and temperature. A thermoelastic plane-stress formulation is used in calculating the stress and deflection of the transducer diaphragm. Both analytical and finite-difference solution methods are available, depending on the sensor structure. Diaphragm thickness taper, oxide and package stress, and rim effects are simulated. For capacitive structures, the program accurately predicts the diaphragm deflection and pressure sensitivity as a function of pressure and temperature. Stepped diaphragm structures are shown to be capable of improving pressure sensitivity by as much as 50 percent. The package-induced thermal drift for electrostatically sealed glass-silicon devices is typically less than 0.05 mmHg/°C.