Bi-FET Cascode Power Switch with Bipolar Drive
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Solution Overview
Problem
Existing power switch devices for high-frequency applications face limitations in current and voltage switching capability, particularly at high voltages, due to the slow switching speed of depletion mode transistors, and are costly when using Gallium Nitride solutions, while alternative solutions with Gallium Arsenide enhancement mode transistors suffer from premature Schottky gate forward turn-on leading to poor power efficiency.
Innovation Solution
A power switch device configuration that includes a depletion mode field effect transistor (D-FET), an enhancement mode field effect transistor (E-FET) in cascode, and a bipolar transistor, where the bipolar transistor drives current to the E-FET to provide charge and increase the Schottky threshold turn-on voltage, allowing for faster switching speeds and reduced costs by using less expensive semiconductor technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a depletion mode JFET or MESFET is used in cascode with enhancement mode MOSFET for high voltage applications, then the device can handle high voltage (>300V), but the switching speed is limited by the slow current and voltage switching capability of the depletion mode transistor
Solution Approach 1:
A bipolar transistor is introduced as an intermediary device between the control signal and the E-FET gate. The bipolar transistor acts as a current amplifier that drives the E-FET gate, enabling fast switching of the depletion mode D-FET while maintaining high voltage handling capability. This mediator resolves the contradiction by providing both the voltage handling of the D-FET and the fast switching of the bipolar transistor.
Solution Approach 2:
The patent employs a composite transistor structure combining different transistor types (bipolar transistor and field effect transistors) in a BiFET configuration. This composite structure integrates the high voltage capability of depletion mode devices with the fast switching of bipolar transistors, achieving both high voltage handling and high switching speed in a single integrated device.
2Speed
If Gallium Nitride (GaN) HEMTs are used for high speed and high voltage switching, then switching performance improves due to higher peak electron velocity and wider bandgap, but the cost increases significantly
Solution Approach 1:
The patent applies local quality by using different semiconductor materials in different regions of the device. The bipolar transistor and E-FET are fabricated using standard silicon or GaAs technology where cost-effective, while only the D-FET requires specialized high-voltage material. This localized approach to material selection achieves high-performance switching without the prohibitive cost of all-GaN construction.
Solution Approach 2:
The invention replaces expensive GaN HEMTs for the bipolar transistor and E-FET portions with cheaper alternative technologies (standard silicon or GaAs). Only the critical high-voltage D-FET portion uses specialized materials, thereby reducing overall manufacturing cost while maintaining the necessary performance characteristics through the hybrid BiFET architecture.
3Ease of manufacture
If a Gallium Arsenide (GaAs) enhancement mode transistor is used in cascode with depletion mode GaN HEMT, then cost is reduced compared to all-GaN solutions, but the lower gate to source threshold voltage causes Schottky turn-on at significantly lower input voltages, degrading power efficiency
Solution Approach 1:
The patent changes the threshold voltage parameter by using a bipolar transistor to drive the E-FET gate instead of directly applying the control signal. The bipolar transistor's base-emitter junction provides a higher turn-on voltage threshold, preventing premature Schottky gate forward turn-on and improving power efficiency while still using cost-effective GaAs or silicon technology for the E-FET.
Data Source
AI summary
Power switch devices for high-speed applications are disclosed. The power switch device includes a depletion mode field effect transistor (D-FET), an enhancement mode field effect transistor (E-FET) and a bipolar transistor. In one embodiment, the E-FET is coupled in cascode with the D-FET such that turning off the E-FET turns off the D-FET and turning on the E-FET turns on the D-FET. Furthermore, the bipolar transistor is operably associated with the D-FET and the E-FET such that turning on the bipolar transistor drives current from the D-FET through the bipolar transistor to the E-FET to provide a charge that turns on the E-FET. The bipolar transistor provides several advantages such as a higher Schottky breakdown voltage for the E-FET and faster current switching speed for the power switch device.