New Transparent Bandpass Filter Using Aluminum Thin-Film Micromesh Structure

Tzu-Chun Tai,Yeong-Her Wang,Cheng-Yuan Hung,Kuan-Jen Lin,Hung-Wei Wu

doi:10.1109/access.2019.2939954

Abstract

In this study, we present the new transparent coplanar waveguide (CPW) bandpass filter using aluminum (Al) thin film micromesh structure. The filter is prepared by the semiconductor process of dc sputtering and standard lift-off technology. In order to achieve the high-performance transparent bandpass filter, the new aluminum thin film micromesh structure with low resistivity to 10 -8 Ω-cm, uniform Al thin film thickness to 3μm, high optical transparent to 78% and simple manufacturing process has been proposed. The transparent bandpass filter is designed at 2.4 GHz with 3-dB fractional bandwidth (FBW) of 5%, the minimum insertion loss (-20 log |S 21 |) of 1.8 dB and the return losses (-20 log |S 11 |) of 25 dB. The simulated and measured results of the transparent bandpass filter are in good agreement. The proposed transparent bandpass filter is showing a simple coplanar waveguide configuration, low thin film resistivity, high thin film transmittance, high filter performance, and small circuit size.

Highlights

Transparent passive microwave components are receiving more attention because of their useful application in transparent 3C products
Many researchers reported achievements related to applying high-transparency and low-resistivity thin film materials such as AgHT-8, indium– zinc–tin oxide (IZTO)/Ag/IZTO (I/Ag/I), indium tin oxide, and gallium-doped zinc oxide
The aluminum thin film micromesh structure is advantageous because it has a low resistivity of 10−8 -cm, a process that is easy for up to 3-μm-thick thin films, high optical transmittance of 78%, and a simple semiconductor manufacturing process

Summary

Introduction

Transparent passive microwave components are receiving more attention because of their useful application in transparent 3C products. Many researchers reported achievements related to applying high-transparency and low-resistivity thin film materials such as AgHT-8, indium– zinc–tin oxide (IZTO)/Ag/IZTO (I/Ag/I), indium tin oxide, and gallium-doped zinc oxide. Some transparent thin-film-based antennas have been reported [1]–[4]. A transparent thin film with high microwave performance should simultaneously satisfy four major conditions: it should be a thick film (satisfy the skin depth of a thin film at an operating frequency), it should have high transmittance (≥70%), it should have low resistivity (∼10−8 -cm), and it should be compatible with the semiconductor process. The critical requirements of an RF component that would enable its wide use are as follows: low cost, high uniform surface of the thin

Methods

Findings

Conclusion