Thermal wavefront imaging using GHz ultrasonics

Abstract

In many cases it is important to measure the temperature and the thermal conductivity of an object by contact. Examples include sensors in robot hands, and sensors to measure material properties during manufacturing. In this paper, we demonstrate the ability to measure the time-of-flight (TOF) as a function of time after mechanical contact to the transducer, and show that the rate of TOF change can indicate the thermal conduction properties of the object being contacted. Using this data we can distinguish different materials with small differences in structure. We have previously reported the use of thin film GHz Aluminum Nitride (AlN) piezoelectric transducers on top of a silicon wafers in configurable ultrasound communications, through-silicon-vias (TSVs), fingerprint sensing, and delay references. Our device is expected to have high yield and reliability owing to elimination of a release step, integration with CMOS and compatibility with CMOS drive voltage (<; 3 Vpp).