JFET Gate Dopant Gradient for Low Pinch-Off Voltage
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Solution Overview
Problem
Existing junction field-effect transistors (JFETs) face challenges in achieving low pinch-off voltage and high output impedance due to limitations in design, such as lack of lateral grading of dopant concentration and incomplete gate region coverage, which also complicates their integration with CMOS technology without compromising performance.
Innovation Solution
The design incorporates a JFET with a drain contact region and a channel region of one conductivity type, surrounded by a gate region of opposite conductivity type, featuring a dopant concentration gradient and field electrodes to enhance pinch-off voltage and output resistance, while being formed using a CMOS process flow to maintain compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a JFET uses a well region as part of a top gate region with lateral pinch off, then the pinch-off voltage can be reduced, but the output impedance becomes poor due to width and depth limitations
Solution Approach 1:
The gate region is divided into two portions with different dopant concentrations: a first portion with higher concentration and a second portion with lower concentration. This local quality variation allows the gate to provide both strong pinch-off capability (from the higher doped region) and high output impedance (from the lower doped region), resolving the contradiction between achieving low pinch-off voltage and maintaining high output impedance.
2Area of stationary object
If some portions of the JFET have no gate region and rely on buried doped regions, then the device area is reduced, but achieving low pinch-off voltage and high conductance becomes difficult due to large channel depth
Solution Approach 1:
The invention transitions from relying solely on vertical channel control to incorporating lateral gate control. The gate region extends laterally adjacent to the channel region, providing pinch-off control in the lateral dimension. This dimensional change allows effective voltage control without requiring deep vertical channels, enabling both low pinch-off voltage and high conductance while maintaining compact area.
3Device complexity
If a JFET relies mainly on well implants for lateral pinch off, then the structure is simplified, but it becomes difficult to achieve both low pinch-off voltage and high output impedance
Solution Approach 1:
The invention changes the dopant concentration parameter within the gate region by dividing it into two portions with different concentrations. The first portion has higher dopant concentration for strong pinch-off, while the second portion has lower dopant concentration for high output impedance. This parameter variation within the gate structure enables simultaneous achievement of low pinch-off voltage and high output impedance without significantly increasing structural complexity.
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 configuration allows for a JFET with improved pinch-off voltage, high output resistance, and high drain saturation current, occupying a relatively small area for its voltage rating, and enables efficient integration with CMOS technology without adverse trade-offs.
Implementation Method 1
a gate region adjacent the channel region and having a second conductivity type opposite the first conductivity type. The first gate region can include a first portion and a second portion, the second portion is disposed between the first portion and the drain contact region, and the second portion has a lower dopant concentration as compared to the first portion
Implementation Method 2
An electronic device can include a junction field-effect transistor (JFET) that can be used as a high voltage transistor. A particular JFET has top and bottom gate regions and relies on pinch off in a vertical direction
Data Source
AI summary
An electronic device can include a JFET that can include a drain contact region, a channel region spaced apart from the drain contact region, and a gate region adjacent the channel region. In an embodiment, the gate region includes a relatively heavier doped portion and a relatively lighter portion closer to the drain contact region. In another embodiment, a gate field electrode can be extended beyond a field isolation structure and overlie a channel of the JFET. In a further embodiment, a region having relatively low dopant concentration can be along the drain side of the conduction path, where the region is between two other more heavily doped regions. In another embodiment, alternating conducting channel and gate regions can be used to allow lateral and vertical pinching off of the conducting channel regions.