Pressure Sensing With PVDF Gated AlGaN/GaN High Electron Mobility Transistor
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1202-I06-03
Pressure Sensing With PVDF Gated AlGaN/GaN High Electron Mobility Transistor Sheng-Chun Hung1, Byung Hwan Chu1, Chih Yang Chang2, Chien-Fong Lo1, Ke-Hung Chen1, Yulin Wang2, S J. Pearton2, Amir Dabiran3, P. P. Chow3, G. C. Chi4 and Fan Ren1 1. Department of Chemical Engineering, University of Florida, Gainesville, Florida 2. Department of Material Sci. and Eng., University of Florida, Gainesville, Florida 3. SVT Associates, Eden Prairie, Minnesota 4. Department of Physics, National Central University, Jhong-Li, Taiwan Abstract AlGaN/GaN high electron mobility transistors (HEMTs) with a polarized Polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an inkjet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 ºC. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change of surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors. Introduction Piezoelectric materials are used widely as sensitive pressure sensors and piezoelectric gauges are typically fabricated with materials such as PZT, lithium niobate and quartz (1-4). In 1969, Kawai found a very high piezoelectric effect in polarized polyvinylidene fluoride (PVDF) (5). Since then, polarized PVDF has also become an important piezoelectric material due to its flexibility, low density, low mechanical impedance and easy fabrication as a ferroelectric. Because of its versatility, PVDF has many applications in low cost and disposable pressure sensors (6). Recently, AlGaN/GaN high electron mobility transistors (HEMTs) have shown great potential for chemical and biochemical sensing applications (7-16). This is due to their high electron sheet carrier concentration channel induced by both piezoelectric and spontaneous polarization (17, 18). Unlike conventional semiconductor field effect transistors, there is no intentional dopant in the AlGaN/GaN HEMT structure. The electrons in the two dimensional electron gas (2DEG) channel are located at the interface between the AlGaN layer and GaN layer and there are positive counter changes at the HEMT surface layer induced by the 2DEG. Slight changes in the ambient can affect the surface charge of the HEMT, thus changing the
2DEG concentration in the channel
(19-25)
.
Thus, nitride HEMTs may be excellent
candidates for pressure sensors and other piezoelectric applications. In this work, we investigated the effect of ambient pressure on the drain current of GaN/AlGaN HEMT sensors with a polarized PVDF thin film coated on the gate area. We quantified the se
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