InP HEMT Pinch-Off Voltage Shift via Metal Ring
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Solution Overview
Problem
The existing FET device fabrication processes require multiple gate recess processing steps to achieve different pinch-off voltages, increasing device cycle time and cost, as they cannot efficiently produce multiple FET devices with varying pinch-off voltages on a single integrated circuit chip.
Innovation Solution
A metal ring is fabricated adjacent to the mesa on HEMT devices operating in enhancement mode, which is integrated during the same processing steps as forming ohmic contacts and gate terminals, altering the pinch-off voltage through electro-chemical effects without additional gate recess etching steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple gate recess processing steps are performed to achieve different pinch-off voltages, then different pinch-off voltages can be achieved, but device cycle time and fabrication cost increase
Solution Approach 1:
A metal ring is formed around the gate terminal during the same processing step as gate recess formation, performing the function of modifying pinch-off voltage in advance. This preliminary action eliminates the need for subsequent additional processing steps to achieve different pinch-off voltages, thereby reducing device cycle time while maintaining the capability to produce multiple pinch-off voltage variants.
Solution Approach 2:
The pinch-off voltage is modified by changing the physical structure through metal ring formation rather than by changing the gate recess depth through multiple etching steps. This parameter change approach allows different pinch-off voltages to be achieved through a single processing step by varying metal ring parameters (material, thickness, geometry) instead of varying gate recess depth through multiple time-consuming etching operations.
2Adaptability or versatility
If multiple gate recess processing steps are performed to achieve different pinch-off voltages, then different pinch-off voltages can be achieved, but fabrication complexity and cost increase
Solution Approach 1:
The formation of the metal ring is merged with the gate recess processing step, combining two functions (gate recess formation and pinch-off voltage adjustment) into a single integrated process. This merging eliminates the need for separate additional processing steps, thereby reducing fabrication process complexity and cost while maintaining the ability to produce devices with different pinch-off voltages on the same wafer.
Solution Approach 2:
The metal ring structure serves multiple functions: it modifies the pinch-off voltage, can be formed in the same processing step as gate recess, and allows for different pinch-off voltages to be achieved through a single universal processing approach. This multi-functionality reduces the overall fabrication complexity compared to performing separate dedicated steps for each pinch-off voltage adjustment.
3Device complexity
If a single gate recess processing step is used, then fabrication complexity is reduced, but the ability to provide multiple pinch-off voltages is lost
Solution Approach 1:
The metal ring acts as an intermediary element that enables pinch-off voltage adjustment without requiring multiple gate recess processing steps. This intermediary structure provides the necessary electrical field modification to achieve different pinch-off voltages while the fabrication process itself remains simple and unified, thus resolving the contradiction between process simplicity and device versatility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for a single gate recess processing step while enabling multiple FET devices on a common substrate to have different pinch-off voltages, reducing fabrication complexity and cost by modifying the pinch-off voltage of HEMT devices using a metal ring, thereby enhancing operational flexibility.
Implementation Method 1
A metal ring is fabricated adjacent to the mesa on HEMT devices operating in enhancement mode, which is integrated during the same processing steps as forming ohmic contacts and gate terminals, altering the pinch-off voltage through electro-chemical effects
Data Source
AI summary
A high electron mobility transistor (HEMT) device comprising a substrate, a plurality of semiconductor layers provided on the substrate, and a source terminal, a drain terminal and at least one gate terminal provided on the plurality of semiconductor layers. The HEMT also includes a metal ring formed on the plurality of semiconductor layers around the source terminal, the drain terminal and the at least one gate terminal, where the metal ring operates to shift the pinch-off voltage of the device. In one embodiment, the metal ring includes an ohmic portion and an electrode portion, where both the ohmic portion and the electrode portion include a lower titanium layer, a middle platinum layer and an upper gold layer.