Working principle of silicon sensors

The working principle of silicon sensors is based on the piezoresistive effect of semiconductors and micromachining technology. A Wheatstone bridge is fabricated on a specific crystal orientation of a single-crystal silicon wafer using semiconductor processes such as photolithography and diffusion to form a sensitive diaphragm. Technicians select a suitable crystal orientation on the (001) or (110) crystal plane of silicon and directly diffuse strain resistors onto the crystal surface. Then, a concave shape is processed on the back side to form a thin silicon elastic diaphragm, called a silicon cup. The silicon chip is electrostatically sealed to a PYREX glass ring. The PYREX glass ring serves as a mechanical fixation support for the elastic sensitive element of the silicon chip and insulates the silicon chip from the package. The holes in the PYREX glass ring become the reference pressure cavity and electrode lead cavity of the sensor. When the sensitive diaphragm is subjected to external force, it generates micro-strain, causing a change in its resistivity. This changes the resistance of the bridge arms of the Wheatstone bridge, resulting in an output electrical signal under the excitation voltage.

Because single-crystal silicon sensors are significantly affected by temperature, compensation technology is required to ensure measurement accuracy. Modern technology uses digital signal processing (ASIC chips) and model algorithms for temperature compensation. With the assistance of a temperature sensor, pressure and temperature values ​​are read in a time-division multiplexing manner. The weak signal is amplified by a programmable gain amplifier, quantized by an ADC, and then fed into a digital processor to calculate the compensated pressure output. All these functional components can be integrated onto a single chip, making it easy to package ASIC circuits and MEMS-based pressure-sensitive chips into a compact housing, thus achieving high-precision measurement over a wide temperature range. Through computer temperature compensation, laser trimming, signal amplification, and other processing methods, along with rigorous assembly, testing, and calibration processes, a pressure transmitter with a standard output signal is finally produced.