Shuyu Wang

Micro-differential scanning calorimeter for liquid biological samples

We developed an ultrasensitive micro-DSC (differential scanning calorimeter) for liquid protein sample characterization. This design integrated vanadium oxide thermistors and flexible polymer substrates with microfluidics chambers to achieve a high sensitivity (6 V/W), low thermal conductivity (0.7 mW/K), high power resolutions (40 nW), and well-defined liquid volume (1 μl) calorimeter sensor in a compact and cost-effective way. We further demonstrated the performance of the sensor with lysozyme unfolding. The measured transition temperature and enthalpy change were in accordance with the previous literature data. This micro-DSC could potentially raise the prospect of high-throughput biochemical measurement by parallel operation with miniaturized sample consumption.

Atomic Layer-Deposited Titanium-Doped Vanadium Oxide Thin Films and Their Thermistor Applications

Here we report the enhancement in the temperature coefficient of resistance (TCR) of atomic layer-deposited vanadium oxide thin films through the doping of titanium oxide. The Hall effect measurement provides a potential explanation for the phenomenon. The composition and morphology of the thin films are investigated by x-ray diffraction and scanning electron microscopy techniques. The high TCR, good uniformity, and low processing temperature of the material make it a good candidate for thermistor application.

A metal-insulator transition study of VO2 thin films grown on sapphire substrates

Vanadium thin films were deposited on sapphire substrates by DC magnetron sputtering and then oxidized in a tube furnace filled with oxygen under different temperatures and oxygen flow rates. The significant influence of the oxygen flow rate and oxidation temperature on the electrical and structural properties of the vanadium oxide thin films were investigated systematically. It shows the pure vanadium dioxide (VO2) state can only be obtained in a very narrow temperature and oxygen flow rate range. The resistivity change during the metal-insulator transition varies from 0.2 to 4 orders of magnitude depending on the oxidation condition. Large thermal hysteresis during the metal-insulator phase transition was observed during the transition compared to the results in literature. Proper oxidation conditions can significantly reduce the thermal hysteresis. The fabricated VO2 thin films showed the potential to be applied in the development of electrical sensors and other smart devices.

Design and Fabrication of Flexible Differential Scanning Nanocalorimeter

This paper discussed about the design and fabrication process of flexible MEMS based Differential Scanning Calorimeter that greatly enhanced the detection limit and accuracy that allowed for evaluation of molecular interaction. The design utilized polyimide to significantly reduce thermal conduction by hundreds of times than traditional used substrate material. Preliminary fabrication result had successfully demonstrated the polyimide membrane can be firmly adhesive on the wafer during fabrication and easily peeled off from the rigid substrate after the process. Temperature sensing material, VOx was prepared by DC magnetron sputter of sintered vanadium target with O2 flow during the sputtering. Deposition conditions such as the O2 flow rate’s influence on the electrical resistivity and temperature coefficient resistance was investigated. The results fully showed that the material prepared by the method has satisfactory performance to be used as thermistor in the calorimeter. Also, research about thermal analysis of the system further guided and confirmed the feasibility of the design.Copyright

A Novel Micro Heater Integrated on Flexible Polyimide Substrate With Fast Response and Uniform Temperature Distribution

This paper presents a novel micro heater prepared on polyimide thin film with fast response and ultra-uniform temperature distribution in the heating area. The transparent polyimide thin film was fabricated by spin-coating, baking and curing the liquid polyimide on the silicon wafer. A gold heater together with the vanadium oxide based thermistor was integrated on the polyimide thin film. Due to the low thermal conductivity of the polyimide thin film, the MEMS heater could reach high temperature with low power consumption and fast response time. FEA method was applied to optimize the shape of the gold heater to achieve uniform temperature distribution along the heating area. A copper island was also deposited on the back of the heater to improve the uniformity of the temperature distribution. The vanadium oxide based temperature sensor with a high temperature coefficient of resistivity as 2.4% was used for the temperature sensing. The temperature variation among the heating area is less than 0.2°C.Copyright

Characterization of a Microfabricated Differential Scanning Calorimeter

Calorimeters are critical tools for structural based drug design and drug stability assessment. Current pharmaceutical industry is seeking for high throughput calorimeters to reduce the research time and expenditure. MEMS-based calorimeter is a potential solution for it, since they are miniaturized to detect the enthalpy change during macro molecular interaction with smaller amount of samples, shorter time and could easily enable parallel measurement. Consequently, we present a Differential Scanning Calorimeter (DSC) that requires 2μL sample volume. It has high thermal insulation (1210μW/K), small time constant (6.95s) and high sensitivity (7.5V/W). The low noise equivalent temperature difference (NETD) could lead to 130nW of power resolution. These characterization results indicate the device could be potentially applied for macromolecular interaction application and increase the throughput with high performance.Copyright