# Monolithic Si-Based AlGaN/GaN MIS-HEMTs Comparator and Its High Temperature Characteristics
###### Abstract  
Monolithic GaN High Electron Mobility Transistor (HEMT)-integrated circuits are a promising application of wide band-gap materials. To date, most GaN-based devices behave as NMOS-like transistors. As only NMOS GaN HEMT is currently commercially available, its control circuit requires special design if monolithic integration is desired. This article analyzes the schematics of a GaN-based comparator, and three comparator structures are compared through ADS simulation. The optimal structure with the bootstrapped technique is fabricated based on AlGaN/GaN Metal-Insulator-Semiconductor (MIS) HEMT with the recessed gate method. The comparator has excellent static characteristics when the reference voltage increases from 3 V to 8 V. Dynamic waveforms from 10 kHz to 1 MHz are also obtained. High-temperature tests from 25 \({}^{\circ}\)C to 250 \({}^{\circ}\)C are applied upon both DC and AC characteristics. The mechanisms of instability issues are explained under dynamic working condition. The results prove that the comparator can be used in the state-of-art mixed-signal circuits, demonstrating the potential for the monolithic all-GaN integrated circuits.  
AlGaN/GaN MIS-HEMT; monolithic comparator circuit; static and dynamic tests; high-temperature stability +
Footnote †: journal: 17 November 2021  
_Accepted: 9 December 2021_  
Footnote †: journal: 17 November 2021  
including NOT, NAND and NOR were reported because of their large noise margin and high-temperature performances [8]. In 2019, GaN power-integrated components and circuits, including HEMTs, Schottky-Barrier Diodes (SBD), Metal-Insulator-Metal (MIM) capacitors and 2 DEG resistors, were successfully implemented on GaN-on-SOI (silicon-on-insulator) to form an integration platform [9]. Compared with the conventional CMOS technology, GaN-integrated circuits focus on integrating different power modules such as power, driver and controller to achieve all-GaN integration, which also occurred when the GaAs IC design was carried out in the 1980s [10; 11]. However, the systematic comparison and optimization of GaN IC design parameters still needs further improvement.  
As an essential part of GaN logic circuits, the comparator draws considerable attention in power electronics for control blocks and power conversion [12]. In 2011, the first GaN comparator circuit was fabricated based on the ion implantation method with DC and AC tests [13]. In 2015, the GaN monolithic comparator was used to perform a PWM circuit, and the hysteresis structure was used to provide feedback from the pulse generation stage to the comparator input [14; 15]. In 2021, the impact of D-mode threshold voltage on the comparator circuit was reported [16].  
Regarding the circuit-level stability test, the impact of threshold instability for the DCFL inverter was reported for the first time in 2021 [17], while the comparator suffers from the same limitations that may cause fault. This article focuses on the circuit-level high-temperature stability of the monolithic AlGaN/GaN MIS-HEMT-integrated comparator. The simulation of three comparator circuits resulted in an optimized circuit structure with good logic conversion characteristics. The static and dynamic results under 250 \({}^{\circ}\)C environments are presented to explore how the high-temperature conditions affect the circuit stability. This comparator indicates the advantages of the integrated circuits for high-temperature applications and provides additional directions for future design.