# A Multilayered GaAs IPD Resonator with Five Airbridges for Sensor System Application

## TL;DR

A new microwave resonator made with gallium arsenide is designed for sensor systems, offering high sensitivity and compact size.

## Contribution

A multilayered GaAs IPD resonator with five airbridges is proposed for high-sensitivity sensor applications.

## Key findings

- The resonator operates at 1.99 GHz with a return loss of 39 dB and a quality factor of 1.15.
- It detects glucose concentrations as low as 0.2 mg/mL with a sensitivity of 14.58 MHz/mg·mL−1.
- The device shows a linear response and short response time suitable for real-time sensing.

## Abstract

This work proposes a microwave resonator built from gallium arsenide using integrated passive device (IPD) technology. It consists of a three-layered interlaced spiral structure with airbridges and inner interdigital structures. For integrated systems, IPD technology demonstrated outstanding performance, robustness, and a tiny size at a low cost. The airbridges were made more compact, with overall dimensions of 1590 × 800 µm2 (0.038 × 0.019 λg2). The designed microwave resonator operated at 1.99 GHz with a return loss of 39 dB, an insertion loss of 0.07 dB, and a quality factor of 1.15. Additionally, an experiment was conducted on the properties of the airbridge and how they affected resistance, inductance, and S-parameters in the construction of the resonator. To investigate the impact of airbridges on the structure, E- and H-field distributions of the resonator were simulated. Furthermore, its use in sensing applications was explored. Various concentrations of glucose solutions were used in the experiment. The proposed device featured a minimum detectable concentration of 0.2 mg/mL; high sensitivity, namely, 14.58 MHz/mg·mL−1, with a linear response; and a short response time. Thus, this work proposes a structure that exhibits potential in integrated systems and real-time sensing systems with high sensitivity.