National Key Laboratory of ASIC, Hebei Semiconductor Research Institute, Shijiazhuang 050051, China
Email: ga917vv@163.com.
In order to address the issue of 220 GHz receiver protection, a single-pole single-throw (SPST) switch based on GaAs PIN diodes is introduced in this research. The PIN diode with an I layer thickness of 400 nm and a cut-off frequency over 1.5THz was created in order to enable the SPST switch to operate in the terahertz frequency range. Therefore, a 220 GHz quasi-MMIC SPST switch was designed using GaAs PIN diodes and a 50 μmthin-film quartz foundry. The measurement reveals that the isolation is > 29 dB, insertion loss is < 3.2 dB in the frequency range of 220 GHz to 230 GHz and IP1dB is 17 dBm at 220 GHz.
Introduction: Switch circuits are crucial for enabling the on-off of signals in millimeter-wave systems including radar, communication, sensing, imaging, and measurement [1]. Applications of switches include transmitters, receivers, time division systems, antennas, etc. Switches need to block the signal with low insertion loss and high isolation, which are used to protect other components of the system.
Switch design is possible using a variety of process technologies. The use of field effect transistors (FET) [2] or diode-based semiconductor [3, 4] processes is a common means of fabricating switches. In addition to these, MEMS techniques [5], phase change materials [6], and 2D materials [7] can be used to enhance the performance of switches. Switches from 220 GHz to 325 GHz are reported using InP DHBT technology with insertion loss of 3.5-4.1 dB and isolation of 36 dB [8]. The switch that can operate at frequencies ranging from 122 GHz to 330 GHz is realized using 50 nm InGaAs mHEMT technology [9], although the isolation and insertion loss are subpar at high frequencies. Compared with those technologies, PIN diodes increase the cut-off frequency by changing the thickness of the I layer, enabling operation at millimeter waves and even higher frequencies.
In this letter, an SPST switch operating at 220 GHz is shown, using 50μm thick quartz circuits and GaAs PIN diodes. The structure of the PIN diode is optimized to reduce the on-resistance and parasitic parameters of the diode, so that the designed SPST switch can work at 220 GHz.
Design of the SPST switch:Figure 1 (a) depicts the structure diagram of the PIN diode designed in this work. Through material structure optimization and the use of an I-layer material structure with a thickness of 400 nm, the PIN diode’s on-resistance is decreased in this study to increase the cut-off frequency of the PIN diode. The parasitic parameters of the PIN diode can be effectively reduced by using the point-supported arched air bridge and the 15 μm substrate thinning process. Figure 1 (b) displays the results of the DC tests performed on the PIN diodes created in this work. Through the extracted junction capacitance and on-resistance, the cut-off frequency (\(f_{c}=\frac{1}{2\pi R_{\text{on}}C_{\text{off}}}\)) [4] of the PIN diode can be calculated to reach more than 1.5 THz, and this PIN diode can work in the terahertz frequency band.