Low on-resistance and high-breakdown-voltage AlGaN/GaN heterostructure field-effect transistors (HFETs) on Si substrate were fabricated. To improve the breakdown voltage of HFET, the total thickness of epitaxial layers was increased and the gate-to-drain spacing was expanded. As a result, the fabricated AlGaN/GaN HFETs with a gate width of 516 mm exhibited a breakdown voltage of 750 V, an on-resistance of 20 m, and a maximum drain current of more than 170 A. The on-resistancearea product (R on  A) was 0.26 Ámm 2 . This value was approximately 1/30 compared with that of conventional Si metaloxide-semiconductor field-effect transistors (MOSFETs).
The normally-off AlGaN/GaN HFETs on Si substrate were fabricated. To realize normally-off characteristic, recess was formed under the gate electrode and NiOx was formed as a gate electrode. As a result, the fabricated AlGaN/GaN HFET with a gate width of 157 mm exhibited a threshold voltage of +0.8 V, a breakdown voltage of more than 800 V, an onresistance of 72 mΩ, and a maximum drain current of more than 20 A. The on-resistance-area product (Ron×A) was 0.28 Ω・ mm 2 . This value is approximately 1/28 compared with that of conventional Si MOSFETs. The gate leakage current was decreased about four orders of magnitude smaller than the conventional normally-on HFETs. The NiOx gate electrode operates as a p-type material.
A new device of high-power AlGaN/GaN heterostructure field-effect transistors (HFETs) fabricated on a Si substrate is proposed. Its application of the power factor correction (PFC) circuit is presented for the first time. The AlGaN/GaN HFETs fabricated on the Si substrate with a gate width of 152 mm exhibited a breakdown voltage of more than 800 V, an onresistance of 65 m, and a maximum drain current of more than 50 A. As for the results of the experiment on the PFC at 200 W and f ¼ 109 kHz, a power conversion efficiency of 95.2% was obtained. This value was about 1% higher than that of the PFC-circuit-using Si devices.
A micro fluorescent analysis system is proposed using silicon micromachining. GaN blue light-emitting diode (LED) monolithically integrated on a silicon substrate is used as a light source for the fluorescent analysis system. The blue light suits the excitation of several dyes used commonly in fluorescent analysis. Silicon photodiode (Si-PD) that matches the visible and near infrared fluorescent wavelengths of dyes is integrated on a silicon substrate. Polydimethylsiloxane (PDMS) micro-channels are also stacked for flowing dye-sensitized liquid. Therefore, the proposed system is an integrated system that can be composed on a silicon platform, i.e. a bottom layer of Si-PD, a middle layer of GaN-LED on silicon substrate and a top layer of micro PDMS channel. An aperture is opened into the GaN-LED layer by deep reactive ion etching to create a ring-shaped GaN-LED and a through-hole for detection. The light from the ring-shaped GaN-LED in the middle layer excites the dye-sensitized liquid in the top micro-channel layer. The fluorescence emitted from dye is detected by the Si-PD on the bottom layer at an angle larger than 90 degrees from the direction of excitation. Therefore, the detection optics consist basically of a dark-field illumination optical system. In order to evaluate the performance of the integrated system, fluorescence of fluorescein isothiocyanate (FITC) solution flowing in the micro channel is measured. From the measurement, the noise, sensitivity and limit of detection in the fabricated system are evaluated for FITC dye to be 0.57 pA, 1.21 pA μM(-1) and 469 nM, respectively. From these results, a compact fluorescence analysis system is demonstrated.
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