7. Design of Novel Thermal MEMS
William P. King and Ajit M. Chaudhari
The MEMS community is introducing a wealth of microfabricated sensors, actuators, and microfluidic devices whose functionality relies on heat transfer. As researchers attempt to optimize these devices, they are encountering limitations in the experimental and theoretical tools that are used for macroscopic systems. This project aims to develop rigorous thermal analysis and experiments that aid with the design of MEMS structures.
One example is our effort on liquid-crystal thermometry of micromachined silicon vessel arrays for DNA replication, which are being developed at Perkin-Elmer Applied Biosystems. The replication is achieved through polymerase chain reaction (PCR), which requires precise cycling of the liquid sample temperature between 55 and 95 oC. PCR using micromachined structures, such as that shown in Figure 1, promises improved temperature uniformity and cycling time together with decreased reagent and sample volumes. Thermal design of these structures requires measurements of the temperature distribution in the reacting liquid. This project uses encapsulated liquid crystals suspended in the liquid to measure temperature uniformity and the time constant for 18 vessels in a micromachined silicon array. Two separate sets of crystals are used to image temperature variations near the two processing temperature thresholds with resolution of 0.1 oC. While the thermometry technique developed here is particularly useful for characterizing microfabricated PCR systems, it can also aid with the thermal design of a broad variety of microfluidic devices.
Another example is the thermal design of silicon cantilevers for high-density thermomechanical data storage using the atomic force microscope (AFM). The cantilevers have been developed by B. W. Chui from the group of Professor T. W. Kenny at Stanford University in collaboration with researchers at IBM Corporation. The cantilever tip exerts a constant force on a polycarbonate sample and induces localized softening and deformation during brief heating events, which are caused by a bias current along the cantilever. The resulting indentations serve as data bits which are read using a separate cantilever with an integrated piezoresistive displacement sensor. The time constant for cooling of the heated cantilever tip governs the rate at which it can achieve sub micrometer writing.
Collaboration
Group of Professor T. W. Kenny, Mechanical Engineering Department,
Stanford University
Applied Biosystems, Incorporated. EG&G IC Sensors. IBM Research
Lab, Zurich.
Recent Publications
Chaudhari, A., Woudenberg, T., Albin, M., and Goodson, K. E., "Transient Liquid Crystal Thermometry of Microfabricated PCR Vessel Arrays," submitted to the ASME/IEEE Journal of MicroElectroMechanical Systems.
Chui, B.W., Stowe, T.D., Ju, Y.S., Goodson, K.E., Kenny, T.W., Mamin, H.J., Terris, B.D., Ried, R.P., and Rugar, D., 1998, "Low-Stiffness Silicon Cantilevers with Integrated Heaters and Piezoresistive Sensors for High-Density AFM Thermomechanical Data Storage," ASME/IEEE Journal of MicroElectroMechnical Systems, Vol. 7, pp. 69-78.
Touzelbaev, M.N., and Goodson, K.E., 1998, "Applications of Micron-Scale Passive Diamond Layers for the IC and MEMS Industries," Diamond and Related Materials, Vol. 7, pp. 1 - 28.
Sponsorship
EG&G IC Sensors
ONR Grant 96-1-0688 (Young Investigator Award, Electronics Division)