Theoretical Analysis and Experimental Study of a Novel CMOS Chip for Measuring Thermal Diffusivity of Liquids

Abstract

The purpose of this dissertation is to design a novel microdevice for measuring the thermal conductivity of a liquid droplet in small amounts. The CMOS chip is fabricated by VIS 0.5 μm 2P3M CMOS process and post-CMOS micromachining processes are proceeded. The CMOS chip consists of a thin film of polysilicon that covers a cavity of the substrate. The thin film has a rectangular centered heater and four temperature sensors that are located at different locations from the heater. Once a known voltage is applied to the heater, the thermal conductivity of liquid drop that spreads over the heater and the temperature sensors can be determined from the measured temperature responses at different locations of the temperature sensors. This study provides theoretical predictions of temperature responses that are obtained from the diffusion equation of a semi-infinite cylindrical model. The experimental and theoretical analysis results illustrate that the higher thermal conductivity of liquid causes the smaller resistance variation of the temperature sensor, and have larger time constant to steady state.