Abhijeet V. Chavan

Batch-processed vacuum-sealed capacitive pressure sensors

This paper reports two multitransducer vacuum-sealed capacitive barometric pressure sensors, one using single-lead and the other using multiple-leads to transfer the electrical signal out of the vacuum-sealed reference cavity. The first device operates with a resolution of 37 mtorr over a pressure range from 600 to 800 torr. The sensitivity is 27 fF/torr (3000 ppm/torr). The TCO at 750 torr is 3900 ppm//spl deg/C and the TCS is 1000 ppm//spl deg/C. The second device has a resolution of 25 mtorr over a range from 500 to 800 torr, with individual transducer sensitivity of 39 fF/torr. The TCO at 750 torr is 1350 ppm//spl deg/C and TCS is 1000 ppm//spl deg/C. Both devices have an on-chip compensation capacitor and are read out using an electronically-trimmed switched-capacitor charge integrator.

A generic multielement microsystem for portable wireless applications

An open-architecture microsystem that can be populated with a variety of sensors and actuators is described. The microsystem is designed for low-power wireless applications where small size and high sensor accuracy are important. It consists of an in-module microcontroller connected to multiple front-end transducers through an intramodule sensor bus. An external interface allows internally processed data to be output through either a hard-wired input/output port or a radio-frequency transmitter. The present microsystem is configured for environmental monitoring and measured temperature, barometric pressure, relative humidity, and acceleration/vibration. It occupies less than 10 cc, consumes an average of 530 /spl mu/W from 6 V, and transmits data up to 50 m. System features such as active power management, the intramodule sensor bus, generic bus interface circuitry, and in-module sensor compensation based on bivariate polynomials are discussed.

A monolithic fully-integrated vacuum-sealed CMOS pressure sensor

This paper presents an integrated multi-transducer capacitive barometric pressure sensor that is vacuum-sealed at wafer level. The interface circuitry is integrated directly within the sealed reference cavity, making the device immune to parasitic environmental effects. The overall device process merges CMOS circuitry with a dissolved-wafer transducer process and is compatible with bulk- and surface-micromachined transducers. The process employs chemical-mechanical polishing (CMP), anodic bonding, and hermetic lead transfers. The sensor achieves 25 mtorr resolution and is suitable for low-cost packaging. It is composed of a programmable switched-capacitor (SC) readout circuit, five segmented-range pressure transducers, and a reference capacitor, all integrated on a 6.5/spl times/7.5 mm/sup 2/ die using 3 /spl mu/m features.

A batch-processed vacuum-sealed capacitive pressure sensor

This paper reports a multi-transducer vacuum-sealed capacitive barometric pressure sensor. The device operates with a resolution of 25 mTorr over a pressure range from 600 to 800 Torr. The sensitivity is 27 fF/Torr (3000 ppm/Torr). The TCO at 750 Torr is 3969 ppm//spl deg/C and the TCS is about 1000 ppm//spl deg/C. The device uses a single layer of polysilicon both for sealing to the glass and for transfer of the glass electrode in the reference cavity to the outside world. The device is read out using a switched-capacitor charge integrator and an on-chip compensation capacitor.

Programmable mixed-voltage sensor readout circuit and bus interface with built-in self-test

As integrated sensors and microactuators are combined with embedded microcontrollers to form microsystems, there is an increasing need for highly-accurate interface circuits to provide the transducers with bus compatibility, programmable control, and self-test. Several readout circuits for capacitive sensors have been reported recently, including a generic interface that has been used extensively in a multi-element microsystem. This paper reports a bus-compatible interface chip that introduces several additional features, including a programmable mixed-signal mixed-voltage switched-capacitor (SC) read-out circuit with self-test and on-line calibration capabilities. This 4.5/spl times/4.5 mm/sup 2/ chip is in a 1 /spl mu/m n-well BiCMOS 2P/2M process with high-voltage CMOS, large-value resistor, and nonvolatile memory options.

A Mixed-Voltage Sensor Readout Circuit With On-Chip Calibration and Built-In Self-Test

This paper reports a mixed-voltage mixed-signal chip for interfacing multiple capacitive transducers to embedded processors in integrated microsystems. A programmable switched-capacitor readout circuit accommodates capacitive sensors from 16 fF to 40 pF and allows self-test and online calibration. The 20 mm2 chip has a sensitivity of 1.25 mV/fF and is realized in a 1 mum n-well BiCMOS 2 P/2 M process that permits high-voltage operation, large-value resistors, and nonvolatile on-chip memory. An on-chip charge pump generates voltages up to 30 V that permits transducer electrostatic self-test. In normal operation mode, the chip provides a fast sensor readout consuming only 90 nj of energy, making it suitable for portable applications.

Non-linear temperature compensation for a micromachined bi-directional thermal flow sensor

Thermal flow sensors have been developed for a variety of applications over the years. Their application in automotive environments with high accuracy, has been challenging due to the large (-40 to 125C) temperature range. To achieve an accuracy of 2% over this temperature range, special sensor construction, flow tube geometry and/or elaborate electronic compensation is required. We present here a mixed analog/digital compensation technique with non-linear TCO (Temperature Coefficient of offset) correction capability for a constant temperature Bi-directional airflow sensor. The resulting system achieves sensitivity of 3mv/% mass flow at idle flow rates (2-5 gm/sec) with an accuracy of 2% over a flow range of 2gm/sec - 100 gm/sec and intake temperature range.