Abstract
A high Q-factor (quality-factor) spiral inductor fabricated by the CMOS (complementary metal oxide semiconductor) process and a post-process was investigated. The spiral inductor is manufactured on a silicon substrate. A post-process is used to remove the underlying silicon substrate in order to reduce the substrate loss and to enhance the Q-factor of the inductor. The post-process adopts RIE (reactive ion etching) to etch the sacrificial oxide layer, and then TMAH (tetramethylammonium hydroxide) is employed to remove the silicon substrate for obtaining the suspended spiral inductor. The advantage of this post-processing method is its compatibility with the CMOS process. The performance of the spiral inductor is measured by an Agilent 8510C network analyzer and a Cascade probe station. Experimental results show that the Q-factor and inductance of the spiral inductor are 15 at 15 GHz and 1.8 nH at 1 GHz, respectively.
Highlights
Micro inductors can be applied in VCO, LC tank and DC-DC converters [1,2]
The results revealed that the distance between the spiral inductor and silicon substrate was about 121 μm
The results proved that the underlying silicon substrate was removed resulting in the Q-factor of the inductor increased
Summary
Micro inductors can be applied in VCO, LC tank and DC-DC converters [1,2]. The Q-factor is an important characteristic for inductors. The spiral inductors with the rectangular and circular shape were built on the 2 kΩ⋅cm silicon substrate using the conventional CMOS process without any post-process, and the maximum Q-factor of the inductors was 12. The post-process employed a wet etching to etch the sacrificial metal layers, and TMAH was adopted to remove the underlying silicon substrate. The post-CMOS process includes an anisotropic RIE CHF3/O2 dry etching to etch the dielectric layer and an isotropic RIE SF6/O2 dry etching to remove silicon substrate for releasing the suspended spiral inductor, in which the spiral inductor had a maximum Q-factor of 7. Micro devices made by the CMOS-MEMS technique usually need a post-process to release suspended structures [12,13] or to add functional films [14]. In order to enhance the Q-factor of the inductor, a post-process is adopted to remove the underlying silicon substrate. Experiments indicate that the suspended spiral inductor has a Q-factor of 15 at 15 GHz
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