HEMT Cap Layer Layout for Stable Pinch-Off Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional junction field-effect transistors (JFETs) and depletion-mode metal-insulator-semiconductor field-effect transistors (D-mode MISFETs) face issues with unstable pinch-off voltage and interface traps due to variations in well region formation and etching depth, leading to unreliable performance in AC/DC power converters and drivers.
Innovation Solution
A high electron mobility transistor (HEMT) structure integrating enhancement-mode (E-mode) and depletion-mode (D-mode) HEMTs is developed, utilizing a compound semiconductor cap layer layout to achieve lateral depletion without additional process steps, allowing precise control of threshold voltage through gap width adjustments between cap layer segments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional JFETs are used to provide start-up function, then the pinch-off voltage can be controlled, but the well region varies by fabrication process leading to unstable pinch-off voltage
Solution Approach 1:
The patent changes the structural parameter from a conventional well region to a compound semiconductor cap layer with specific bandgap properties. This parameter change eliminates the fabrication-induced variation in pinch-off voltage by using the inherent electrical properties of the semiconductor material instead of relying on geometric well region dimensions that are difficult to control precisely.
2Reliability
If D-mode MISFETs are used to provide start-up function, then depletion-mode operation is achieved, but gate recess etching depth cannot be precisely controlled leading to unstable threshold voltage
Solution Approach 1:
The patent extracts the gate recess formation step from the fabrication process. Instead of forming a gate recess and filling it with dielectric material, the invention uses a compound semiconductor cap layer that naturally provides the depletion-mode characteristics without requiring the complex gate recess structure, thereby eliminating the etching depth control issue.
Solution Approach 2:
The patent changes the gate structure from a metal-insulator-semiconductor configuration requiring gate recess to a compound semiconductor cap layer configuration. This parameter change eliminates the need for precise gate recess etching depth control while achieving the same depletion-mode functionality through the inherent electrical properties of the semiconductor material.
3Reliability
If D-mode MISFETs are used, then depletion-mode operation is achieved, but interface traps are produced between gate dielectric layer and semiconductor layer reducing reliability
Solution Approach 1:
The patent extracts and eliminates the gate dielectric layer from the structure. By using a compound semiconductor cap layer directly on the channel layer, the invention removes the interface between gate dielectric and semiconductor that causes interface traps, thereby improving reliability without adding complex manufacturing steps.
Solution Approach 2:
The patent uses a compound semiconductor cap layer with specific bandgap properties (higher than the channel layer) to achieve the depletion-mode characteristics. This composite semiconductor structure provides both the electrical functionality and the interface quality improvement by eliminating the need for separate gate dielectric material.
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
The HEMT structure provides stable and precise electrical characteristics, overcoming interface trap issues and achieving precise control of pinch-off voltage, thereby enhancing reliability and performance in power converters and drivers.
Implementation Method 1
A layout of a compound semiconductor cap layer of the HEMT structure is used to achieve the effect of lateral depletion
Data Source
AI summary
A high electron mobility transistor structure includes a compound semiconductor channel layer disposed on a substrate, a compound semiconductor barrier layer disposed on the compound semiconductor channel layer, and a compound semiconductor cap layer disposed on the compound semiconductor barrier layer. The compound semiconductor cap layer includes a first segment and a second segment arranged along a first direction, and a gap between the first segment and the second segment. A gate electrode is disposed on the compound semiconductor cap layer. A source electrode and a drain electrode are disposed on the compound semiconductor barrier layer, arranged along a second direction and respectively located on two sides of the compound semiconductor cap layer.