Metal Oxide-Based Monolithic Complementary Metal Oxide Semiconductor Gas Sensor Microsystem

TLDR

The paper presents a fully integrated gas sensor microsystem that combines a micro hot plate with advanced analog and digital circuitry on a single chip. The system is fabricated in a 0.8‑μm CMOS process, with a nanocrystalline SnO₂‑coated micro hot plate, standard micromachining, and a robust package that includes a microcontroller board for communication and power, eliminating the need for external measurement equipment. The prototype achieves a 500 × 500 µm² circular micro hot plate with ±2 % temperature homogeneity, 6.0 °C/mW thermal efficiency, on‑chip temperature control accurate to ±2 °C over 170–300 °C, a logarithmic converter spanning 1 kΩ–10 MΩ, and sub‑ppm CO detection with ±0.1 ppm resolution.

Abstract

A fully integrated gas sensor microsystem is presented, which comprises for the first time a micro hot plate as well as advanced analog and digital circuitry on a single chip. The micro hot plate is coated with a nanocrystalline SnO2 thick film. The sensor chip is produced in an industrial 0.8-μm CMOS process with subsequent micromachining steps. A novel circular micro hot plate, which is 500 × 500 μm2 in size, features an excellent temperature homogeneity of ±2% over the heated area (300-μm diameter) and a high thermal efficiency of 6.0 °C/mW. A robust prototype package was developed, which relies on standard microelectronic packaging methods. Apart from a microcontroller board for managing chip communication and providing power supply and reference signals, no additional measurement equipment is needed. The on-chip digital temperature controller can accurately adjust the membrane temperature between 170 and 300 °C with an error of ±2 °C. The on-chip logarithmic converter covers a wide measurement range between 1 kΩ and 10 MΩ. CO concentrations in the sub-parts-per-million range are detectable, and a resolution of ±0.1 ppm CO was achieved, which renders the sensor capable of measuring CO concentrations at threshold levels.