A microbolometer-based scanning thermal microscopy system with servo-controlled interface circuitry

A scanning thermal microscopy system with micromachined bolometer-type probes and a custom interface circuit was designed and implemented. This represents the second generation of development in the evolution of this microscopy system. The first generation focused on proof of concept and used an open loop interface circuit. The new interface circuit features temperature controllability and temperature dithering to accomplish a high signal-to-noise ratio. It was successfully applied to scanning thermal microscopy and microcalorimetry of various samples.; The micromachined bolometer probe has strong potential in realizing a scanning thermal microscopy system with high resolution and wide applications and in characterizing thermal properties of nano-patterned material by virtue of its small tip area and compliant probe shank. The thermal interaction between the probe and circuit was modeled using the equivalent electrical model. Unified simulation of the transducer and circuit was utilized to predict the performance of the system.; The probe design and the 6-mask fabrication process were further developed and refined over the first generation. The probe structure was optimized in regard to sensitivity, probe stiffness, and thermal response time based on theoretical analysis. Typical probe dimensions are 250–500 μm length, 50–200 μm width, and 3.5 μm thickness. The probes are ultra-compliant with a spring constant of 0.082 N/m, which can be further reduced by changing the material and/or dimensions. The probe offers lateral spatial resolution of <50 nm, topographical resolution of 7 nm, and tip temperature resolution less than 2.5 mK.; The interface circuit features temperature controllability and temperature dithering, showing that high resolution can be obtained both in the DC closed loop and the AC dithering circuit operating conditions. The probe temperature can be precisely controlled by a PI controller while electrical dithering provides relative immunity to thermal bridge noise even for sub-μV low-frequency signals. Scanning thermal images obtained showed a high signal-to-noise ratio of 16 for 350 nm UV photoresist in which the resolvable thermal conductance change was 2.3 × 10−11 W/K.