High performance scanning thermal probe using a low temperature polyimide-based micromachining process

This paper describes scanning thermal probes that exploit the low thermal conductivity and the high mechanical flexibility of polyimide as a structural material. They are surface micromachined using a low-temperature 6-mask process suitable for appending to a CMOS fabrication sequence. The probes are 200-1000 μm long, 40-120 μm wide, and of varying thickness. They are assembled by a flip-over approach that obviates the need for dissolving the substrate wafer or removing the probe from it. Temperature sensing is provided by thin-film Ni/W thermopiles embedded in the polyimide. Measurements indicate temperature sensitivity of 6 μV/K, and bandwidth of 500 Hz. Modeling results indicate that the polyimide provides almost 10× larger temperature sensitivity than a Si probe of equal dimensions. A sample scan is presented