Static Induction Transistor Gate Bus Extension for High Breakdown Voltage
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Solution Overview
Problem
Conventional static induction transistors (SITs) have gate-to-drain breakdown voltages limited to hundreds of volts, which is insufficient for many applications requiring thousands of volts.
Innovation Solution
A semiconductor structure with a substrate and multiple layers of varying dopant concentrations, where p+ gate regions and guard rings are ion implanted, and the gate bus is connected to a layer of lower dopant concentration using a self-aligned ion implantation technique, enhancing the gate-to-drain breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SIT structure is used, then manufacturing is simple, but gate-to-drain breakdown voltage is limited to hundreds of volts
Solution Approach 1:
The semiconductor structure is divided into multiple layers with different dopant concentrations: a first semiconductor layer with lower dopant concentration and a second semiconductor layer with higher dopant concentration. This segmentation allows the gate bus extension to connect to the lower dopant concentration first layer, thereby achieving higher gate-to-drain breakdown voltage while managing the complexity through structured layering
Solution Approach 2:
Different regions of the semiconductor structure are assigned different dopant concentrations tailored to their specific functions. The first layer has lower dopant concentration optimized for high breakdown voltage where the gate bus extension connects, while the second layer has higher dopant concentration optimized for current conduction. This local quality differentiation resolves the contradiction by optimizing each region for its specific purpose
2Manufacturing precision
If ion implantation is used for gate formation, then precise doping is achieved, but misalignment may occur
Solution Approach 1:
The method employs a self-aligned ion implantation process where the gate bus extension is formed first, and subsequent gate ion implantation is automatically aligned to the previously formed structures. This preliminary action of creating alignment references before final doping ensures precise ion implantation positioning, preventing misalignment and reducing gate-to-source leakage current
Solution Approach 2:
The ion implantation process is designed to be self-aligning, where the previously formed gate bus extension and layer structures automatically serve as alignment guides for subsequent implantation steps. The process uses the existing structure geometry itself to define the precise implantation locations, eliminating the need for separate alignment procedures and ensuring manufacturing precision
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 structure achieves significantly higher gate-to-drain breakdown voltages in the thousands of volts, while reducing gate-to-source leakage current and ensuring precise ion implantation without misalignment.
Implementation Method 1
p+ gate regions and guard rings are ion implanted, and the gate bus is connected to a layer of lower dopant concentration using a self-aligned ion implantation technique
Data Source
AI summary
A structure for use in a static induction transistor includes a semiconductor body having first and second semiconductor layers on a substrate, with the second layer having a dopant concentration of around an order of magnitude higher than the dopant concentration of the first layer. A plurality of sources are located on the second layer. A plurality of gates are ion implanted in the second layer, an end one of the gates being connected to all of the plurality of gates and constituting a gate bus. The gate bus has an extension connecting the gate bus in the second layer of higher dopant concentration to the first layer of lower dopant concentration. The extension is ion implanted in either a series of steps or a sloping surface which is formed in the first and second layers.