Abstract-Surface passivation of high-resistivity silicon (HRS) by amorphous silicon thin-film deposition is demonstrated as a novel technique for establishing HRS as a microwave substrate. Metal-oxide-silicon (MOS) capacitor measurements are used to characterize the silicon surface properties. An increase of the quality factor (Q) of a 10-nH spiral inductor by 40% to = 15 and a 6.5-dB lower attenuation of a coplanar wave guide (CPW) at 17 GHz indicate the beneficial effect of the surface passivation for radio frequency (RF) and microwave applications. Regarding CPW attenuation, a nonpassivated 3000-cm substrate is equivalent to a 70-cm passivated substrate. Surface-passivated HRS, having minimum losses, a high permittivity, and a high thermal conductivity, qualifies as a close-to-ideal radio frequency and microwave substrate.
Abstract-This paper addresses the properties of a surface-passivated (enhanced) high-resistivity silicon (HRS) substrate for use in monolithic microwave technology. The detrimental effects of conductive surface channels and their variations across the wafer related to the local oxide and silicon/silicon-dioxide interface quality are eliminated through the formation of a thin amorphous layer at the wafer surface. Without passivation, it is found that the surface channels greatly degrade the quality of passive components in HRS by masking the excellent properties of the bulk HRS substrate and by causing a spread in parameters and peak values across the wafer. Moreover, it is seen that the surface passivation leads to excellent agreement of the characteristics of fabricated components and circuits with those predicted by electromagnetic (EM) simulation based on the bulk HRS properties. This is experimentally verified for lumped (inductors and transformers) and distributed (coplanar waveguide, Marchand balun) passive microwave components, as well as for a traveling-wave amplifier, through which also the integration of transistors on HRS and the overall parameter control at circuit level are demonstrated. The results in this paper indicate the economically important possibility to transfer microwave circuit designs based on EM simulations directly to the HRS fabrication process, thus avoiding costly redesigns.Index Terms-High-resistivity silicon (HRS), inductors, Marchand balun, substrate passivation, transformers, traveling-wave amplifier (TWA).
We present an investigation of the electrical characteristics of plasma exposed GaN. The specific contact resistance of ohmic contacts fabricated on GaN after argon plasma bombardment for 2.5 min at 0.03 W/cm2 are measured to decrease by a factor of 4 compared to the unetched surface. Gold has been found to be the best material for GaN Schottky diode. A study of the electrical performance of diodes fabricated on plasma exposed GaN has been undertaken. To compare the effect of the chemical versus physical factors, as well as the role played by the ion mass of the etchant species during the etching process on diode behavior, GaN surfaces have been exposed to Ar, N2, as well as SF6+N2 plasmas before diode fabrication. Our data indicate that a plasma with low ion mass etchant species or a dominant chemical mechanism of etching with a high etch rate creates less surface damage. The use of a SF6+N2 plasma should be possible for GaN transistor gate recessing.
Dry etch behavior in the inductively coupled plasma processing of GaN using SF6/N2 plasma has been found to be highly ion induced with an ion energy threshold of about 100 eV. Temperature dependence of the etch rate indicates a small kinetic component. Maximum etch rate of 67 nm/min and good anisotropy have been demonstrated. The most efficient etch regime is observed for an ICP source power between 500–1000 W where the etch mechanism is ion limited. In contrast to reactive ion etching induced damage behavior, almost ideal diodes are obtained at the higher dc bias condition (300 V). X-ray photoelectron spectroscopy and atomic force microscopy studies indicate that smooth surface with minimal surface contamination, coupled with the incorporation of N on the substrate surface help to produce ideal diodes on surfaces etched at 300 V. Sidewall depletion is found to be in the range of 65 nm at the given SF6/N2 plasma process conditions.
We have developed a process using electron beam lithography and reactive ion etching for the high resolution pattern transfer of GaN. 150 nm dots have been fabricated in GaN successfully. Photoluminescence, scanning electron microscopy, and x-ray photoelectron spectroscopy have been employed to compare the damage inflicted on the GaN surfaces after SF 6 and Ar plasma exposures. Near-band-edge luminescence analysis indicates the existence of a higher concentration of donors on the top 100 nm of the GaN surface after Ar as supposed to SF 6 plasma exposure. An order of magnitude decrease in the ratio of the yellow to the band-edge luminescence intensity is found in the samples subjected to lower ion energies. Formation of pits is observed on the substrate surfaces after plasma treatment. Nitrogen deficient surfaces limited to the top few monolayers, as well as defect propagation down to 100 nm, exist in our plasma exposed GaN samples.
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