MEMS probes for on-wafer RF microwave characterization of future microelectronics: design, fabrication and characterization

Abstract

This article presents microelectromechanical system (MEMS) ground-signal-ground (GSG) probes based on silicon-on-insulator (SOI) technology for on-wafer microwave characterization of radio-frequency (RF) microelectronics. The probe is designed using optimized coplanar waveguide structures with the aim of ensuring a low-contact resistance between the probe and the pads of the device under test (DUT). The probes are batch fabricated using SOI substrates and employ a simple silicon micromachining process. The probes have a pitch of 4.5 µm with miniaturized dimensions for a DUT pad area with a similar size. Electrical (dc) measurements show that the fabricated probe has a low-contact resistance (~0.02 Ω) on gold pads. Excellent extracted RF performances of the probe are observed up to 30 GHz, showing an insertion loss better than 2.2 dB and return loss better than 20 dB over the frequency range. An ageing study shows the probes are capable of forming this dc contact for over 6000 contact cycles. The preliminary result of the repeatability of on-wafer one-port measurements with the miniaturized probe shows a consistent RF performance maintained through several contacts. The data indicates that the proposed MEMS probe is suitable for the high-frequency characterization of integrated nanoscale devices having reduced pad dimensions.

On overtravel and skate in cantilever-based probes for on-wafer measurements

“…In contrast, the overtravel-to-skate relationship is different and somewhat subtler for microcantilever-based surface contact probes [13][14][15]. The reason for this is that a microcantileverbased probe, e.g.…”

Intertrack surface losses in miniature coplanar waveguide on silicon-on-insulator

“…The silicon dioxide was annealed in N2 at a temperature of 1000°C for 60 minutes. Following this, the metallic CPW tracks were deposited onto the surface of the wafers using evaporated chromium/gold (thickness: 10/500 nm) bilayer patterned via electron beam (ebeam) lithography and lift-off techniques [6]. A Cr/Au metallization was used as it is relatively chemically resistant to aqueous solutions of hydrofluoric (HF) acid [28]-the wafers were to be treated with a 'buffered' HF solution later in the study.…”

“…Coplanar waveguides (CPW) [1,2] have long been a key component in radio frequency (RF) circuits and integrated circuits (IC) [3]. CPW are also important elements in emerging technologies such as quantum computing [4] and associated circuitry [5], miniature microelectromechanical systems (MEMS) based probe technologies [6], non-invasive biosensors [7], and for high frequency characterization of a variety of materials [8][9][10][11][12]. An understanding of signal attenuation (due to losses) in CPW is therefore critical for both RF circuits [13,14] and for emerging applications [15,16], which can involve miniature CPW [16][17][18] to enhance performance-where characterization and understanding of losses are relatively less-well documented.…”

Passivation of miniature microwave coplanar waveguides using a thin film fluoropolymer electret

“…Coplanar waveguides 1 (CPW) are now common place in microwave electronic circuitry 2 – 4 . As is the case of most electrical and electronic components, miniaturization of CPW is proving beneficial in many applications areas, ranging from high-frequency telecommunications 5 , 6 , and emerging miniaturized tools 7 for their automated characterization 8 , to quantum computing 9 , 10 and biosensors 11 . In as much, both a physical understanding and a technological control of signal attenuation are major issues in future CPW engineering.…”