Adaptive Calibration and Quality Control of Smart Sensors

Abstract

Smart sensors represent an attractive approach in sensor applications due to their adaptability, achieved by means of digital signal processing. Sensor adaptability can be further turned into a major advantage by introduction of smart calibration systems. Smart sensors are generally integrated with signal conditioning circuits. Signal conditioning circuits are needed to adjust the offset voltage and span, for compensation of temperature effects of both offset voltage and span, as well as to provide an appropriately amplified signal. The proposed approach is based on a special case of smart pressure sensors, but the developed calibration system is generally applicable for any kind of smart sensor. In manufacturing of modern electronic devices achieving and maintaining high yield level is a challenging task, depending primarily on the capability of identifying and correcting repetitive failure mechanisms. Yield enhancement is defined as the process of improving the baseline yield for a given technology generation from R&D yield level to mature yield. Yield enhancement is one of the strategic topics of ITRS (International Technology Roadmap for Semiconductors, Test And Test Equipment, 2006). This iterative improvement of yield is based on yield learning process, which is a collection and application of knowledge of manufacturing process in order to improve device yield through the identification and resolution of systematic and random manufacturing events (International Technology Roadmap for Semiconductors, Yield Enhancement, 2006). Yield improvement process will consequentially increase the number of test parameters and hence the calibration system complexity. One of advantages of increasing system complexity is the ability to integrate the input testing processes and output final testing processes into the calibration process itself, thus shortening the total time for calibration. Several types of smart sensors with integrated signal conditioning have been presented over the past few years (Takashima et al., 1997) & (IEEE Std. 1451.2 D3.05, 1997). The calibration processes and temperature compensating methods for these sensors are based either on analog, digital or mixed approaches. Analog approach usually comprises an amplifier with laser trimmable thin film resistors (Chau et al., 1997) & (Wang et al., 2005) or off-chip trimmable potentiometers (Schnatz et al., 1992) & (Lee et al., 1999), to calibrate the sensor span and offset voltage and to compensate for their temperature drift. Analog compensation