Submicron-scale surface acoustic wave resonators fabricated by high aspect ratio X-ray lithography and aluminum lift-off

Abstract

A submicron-scale surface acoustic wave (SAW) resonator fabricated by high-aspect-ratio X-ray lithography (XRL) and metal lift-off that operates at microwave frequencies is presented. We demonstrate that XRL is especially well suited for SAW device templating, as long submicron-scale interdigitated transducer structures can be batch patterned with excellent structure quality. 0.4-2.0 lm thick PMMA layers were structured by X-ray lithography shadow projection using silicon nitride-based X-ray masks. Structures with a critical lateral feature size of down to 200-700 nm were processed. The polymer structures served as templates in a subsequent aluminum lift-off process. The metal electrodes were successfully tested as SAW resonators for high frequency applications, e.g. around 1.3 GHz, using calibrated 1-port RF wafer probing measurements. Compared with standard fabrication techniques, the high structure quality of submicronscale polymer templates made of unusually thick PMMA layers offers additional possibilities to fabricate thicker metal transducers.

Inducing variable pitch gratings in nematic liquid crystals using chirped surface acoustic wave transducers

“…This continuous variation is promising, although smaller λ dom values would be required to demonstrate potential as DOEs. Existing standard lithography procedures allow SAW devices to be fabricated with submicron feature sizes [47]. If the relation given in equation ( 7) continued into this regime, λ dom below 1 µm would be achievable.…”

Finite element modeling of electrode mass loading effects in longitudinal leaky SAW resonators

“…With a look toward the feasibility of fabrication techniques such as XRL [4] for producing precise high aspect ratio structures, simulations were performed with MR of 0.3 and varying the electrode metal height in an attempt to find an optimal h/ to support LLSAW. Figure 9 shows the magnitude of the admittance response with MR of 0.3 and h/ varied from 6.75 to 8%.…”

“…Certainly, the metal thickness in this case is not negligible, and even small irregularities in electrode thickness and sidewall geometry due to lithography and lift-off errors and also metal thickness deposition inhomogeneity can cause significant variation in electrode mass. As a result, new precision high-aspect ratio microfabrication techniques for realizing thick metal electrode SAW devices, such as deep X-ray lithography (XRL) as demonstrated recently by Achenbach et al [4], could become increasingly important.…”

X-ray fabrication of SAW resonators with narrow electrodes in thick high-aspect-ratio polymer templates

“…X-ray lithography (XRL) is being used to fabricate other high-aspect-ratio RF devices [10][11][12] with novel geometries and high performance, but to date has received limited application for SAW devices. In [13], the feasibility of pattering thick (up to 2 μm) polymethylmethacrylate (PMMA) templates using XRL on silicon wafers representing line-andspace IDT structures for SAW applications at >1 GHz was demonstrated. The line-to-space pitch of the IDT patterns was 1590 nm, and the vertical to lateral aspect ratio of the freestanding 2 μm tall polymer structures was on the order of 2.5:1.…”