Surface-Passivated High-Resistivity Silicon Substrates for RFICs

Abstract

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.

Surface-passivated high-resistivity silicon as a true microwave substrate

“…Consequently, accumulation, depletion, and inversion layer formation will be prevented and the additional source of loss will be eliminated. Such a high trap density can be achieved through a high-dose implantation of a neutral impurity, such as argon [13], [14] into the silicon surface region or by depositing a thin highly defective silicon layer such as poly-crystalline silicon [9] or amorphous silicon [16] onto the wafer. For the experiments presented in this paper, we used an implantation of argon at a dose of 10 cm to form the SP HRS [16].…”

“…This, however, brings several technological issues in focus that may form bottlenecks, in particular the considerable losses in the conventional silicon substrates [6]. Currently, resistivities of at most [10][11][12][13][14][15][16][17][18][19][20] cm [low-resistivitysilicon(LRS)]arebeingused.Thiscorrespondsto conductivities that lead to considerable substrate losses and, thus, to excessive attenuation of integrated transmission lines [7] and reduced quality factors of on-chip inductors [8]. III-V-based processes have ideal substrates in that respect, but these lack other important properties such as high thermal conductivity and high and frequency-independent permittivity that qualify silicon as a true microwave substrate [7].…”

Thermal effects in suspended RF spiral inductors

“…Hence, when high RF or dc power levels are involved, measures have to be taken to facilitate the transfer of heat away from the coil. A possible solution is the use of very thick metal for reduced thermal resistance of the coil or the consideration of inductors built on low-loss, yet thermally well conducting, substrates such as high resistivity silicon [10].…”

Thermal Issues in Micromachined Spiral Inductors for High-Power Applications

“…The best alternative in this case, in fact, is to use nonsuspended coils. In order to provide a coil structure that features both a high Q and a high thermal conductivity to the substrate, one should consider fabricating coils on substrates with low RF loss yet good thermal conductivity, such as HRS [2]- [4]. The comparison of experimental data obtained (see Fig.…”

“…Solutions to the substrate loss include the use of high-resistivity Si (HRS) [2]- [4], thick dielectric layers [5]- [8], proton bombardment of Si [9], [10], and oxidized deep trenches [11], [12]. Although effective, such methods involve major modification of the core device integration process, leading to process incompatibility and, thus, considerably higher cost.…”