Vertical GaN opens up next-generation power supply design – Gate Drive Edition

Narrow down by specifying conditions

現在2201件がヒットしています。check

Design Analog Discrete Power Devices On Semiconductor

Introduction

As GaN is increasingly adopted as a next-generation power device, the ease of design and reliability of gate drive circuits are becoming important differentiating factors.
**Vertical GaN (hereinafter referred to as vertical GaN) **, which has attracted particular attention in recent years, has significant advantages in terms of gate drive requirements compared to conventional SiC MOSFETs and lateral GaN (HEMTs).
This article compares the devices from the perspectives of drive current, circuit configuration, tolerance, and reliability.

Basic structure and effects of each device

device	structure	Impact on gate characteristics
SiC MOSFET	MOS structure (oxide gate)	High Qg and high voltage drive required
Horizontal GaN (HEMT)	AlGaN/GaN hetero	Low Qg, but delicate and prone to malfunctions.
Vertical GaN	GaN-on-GaN + vertical JFET structure	Low Qg + High voltage resistance + High robustness

Table 1: Basic structure and effects of each device

As can be seen in Table 1, vertical GaN does not have a MOS structure in the gate like conventional FETs. Therefore, the gate terminal has very high durability.

Figure 1 shows a vertical GaN model. All capacitance is junction capacitance; there is no MOS capacitance.
To explain it in terms of operation, if the CGD of the FET is a MOS capacitance, the gate voltage rises through the charging of the CGD when the FET is off, causing it to falsely turn on.
In vertical GaN, the CGD is a junction capacitance, so its capacitance increases with the rise in drain voltage VD. However, the rise in gate voltage during CGD charging is instantaneously discharged through the DGS diode, so it does not exhibit false ON operation like MOS-FETs.
Therefore, the mirror clamp circuit that was previously required for gate drives is no longer necessary.
The manufacturer has confirmed that it does not malfunction even at a switching frequency of 10MHz and operates normally.

Drive current and drive circuit

The threshold voltage Vth of vertical GaN is around 2.5V, which is lower than that of SiC. However, as mentioned earlier, it has a structure that is less prone to false on-on, so the drive circuit can be simplified compared to silicon or SiC.

1. Since the gate is not a MOS capacitance, a high-current circuit for instantaneous charging is not required. Although a carrier is necessary for depletion layer disappearance due to the J-FET structure, this device can be fully turned on with a gate current of approximately 100mA.

2. When the device is off, the carrier self-destructs, eliminating the need for a forced discharge (Miller clamp) circuit. Furthermore, a negative voltage bias for the gate is also unnecessary.

3. The gate structure of vertical GaN is a junction structure, making it a current-driven device. The breakdown voltage is determined by the reverse breakdown voltage of the junction. If the sink current capability of the gate driver is optimized, negative voltage is unnecessary as mentioned earlier, so there is no need to consider the gate breakdown voltage in the initial design.

4. Demand for vertical GaN is expected to grow in the future for high-voltage and high-speed switching applications. In particular, we believe that dead-time circuit formation will be a key technology in high-speed gate switching circuits. With silicon and SiC-FETs, the dead time is determined by resistors and diodes, but with vertical GaN, a shorter dead time formation is required, so the circuit will be constructed using high-frequency diodes, resistors, and capacitors.

lastly

For more technical articles related to vertical GaN, please refer to the following articles.

Vertical GaN opens up next-generation power supply design – Why it surpasses silicon /SiC/ horizontal GaN–

Inquiry

If you are interested in the content introduced in this article, please feel free to contact us.

Onsemi Manufacturer information Top

If you want to go back to ONSEMI Manufacturer Information Top, please click below.

Back to Manufacturer Information Top