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.