Suspended diamond air bridge in semiconductor material

Removes waste heat and reduces capacitive coupling between the drain and the gate in High Electron Mobility Transistors (HEMTs)


Navy scientists have improved the thermal management for optoelectronic devices, such as field-effect and high electron mobility transistors. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.

A sacrificial layer (SL) is etched away to leave the suspended diamond air bridge above the passivation layer and portions of the source, gate, and drain, with other portions of the source, gate, and drain having the diamond layer in contact therewith to provide thermal management in those layers. Because of the thickness of the SL, the diamond air bridge is suspended at a greater distance above the structure, particularly above the gate and the drain, which reduces the capacitive coupling between the gate and the drain in the device

The parasitic capacitance between the gate and drain and between the gate and source can significantly affect the efficiency of Gallium-nitride (GaN)-based High Electron Mobility Transistors (HEMT), especially at high frequencies. A key determinant of the capacitance of the gate to the drain, source, and body is the thickness and dielectric constant of passivation materials in the gate-to-drain and gate-to-source regions. A passivation material layer with a lower dielectric constant will have lower gate-to-drain and gate-to-source capacitances.

Improvements in material growth, device design, and device fabrication have enhanced power-added efficiencies. However, GaN HEMTs designed for RF, microwave, millimeter-wave, and power switching applications are severely limited by the ability to dissipate heat and must run at significantly reduced power levels, pulse length, and duty cycle. Past methods to implement thermal management by depositing diamond on electronic devices led to an additional capacitive coupling between the gate and the drain resulting in a loss of gain at high frequencies.

Navy scientists have invented a device structure and method for improving thermal management in highly scaled, high-power electronic and optoelectronic devices such as GaN Field Effect Transistors (FET) and more specifically, AlGaN/GaN HEMT devices. Suspended diamond air bridges between the source and the gate, and between the gate and the drain, remove waste heat. This is achieved by depositing a diamond material layer on a sacrificial layer in a semiconductor heterostructure, which is later removed, leaving only the suspended diamond air bridge.

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