High Voltage Device Lateral Lightly Doped Region Capacitance
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Solution Overview
Problem
High voltage devices, such as DMOS devices, face limitations in transient response due to internal capacitance, which restricts their switching speed and application range.
Innovation Solution
The design incorporates a high voltage device with a first deep well and a high voltage well of opposite conductivity types, along with a lateral lightly doped region and isolation regions, to reduce internal capacitance and enhance switching speed. The manufacturing method involves forming these regions in a semiconductor substrate to define an operation region and optimize the device's structure for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional DMOS device structure is used, then the device can withstand high voltage, but the internal capacitance is high which limits the transient response and switching speed
Solution Approach 1:
The device structure is segmented into multiple regions with different doping concentrations: a lightly doped drift region, a moderately doped body region, and a heavily doped source/drain region. This segmentation allows each region to be optimized for its specific function while reducing overall internal capacitance
Solution Approach 2:
Different regions of the device are given different local properties: the drift region has low doping concentration to reduce capacitance, the body region has intermediate doping for voltage blocking, and the source/drain regions have high doping for efficient carrier injection. This local quality differentiation resolves the contradiction between voltage withstanding and switching speed
2Reliability
If the drift region is made longer to increase voltage blocking capability, then the device can handle higher voltages, but the internal capacitance increases and switching speed decreases
Solution Approach 1:
The doping concentration parameter is changed along the drift region length, creating a gradient from lightly doped near the drain to moderately doped near the body. This parameter change allows the drift region to maintain voltage blocking capability while reducing the capacitance that would otherwise accumulate in a uniformly long drift region
Solution Approach 2:
The problem is solved by adding a vertical dimension to the doping profile, creating a three-dimensional doping distribution that varies both horizontally and vertically. This dimensional approach allows optimized voltage blocking without proportionally increasing capacitance
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 solution effectively reduces internal capacitance, thereby improving the transient response and expanding the application range of high voltage devices by enhancing their switching speed.
Implementation Method 1
when a junction between the P-type body region 105 and the N-type high voltage well 102 is reverse-biased, and/or when a junction between the N-type high voltage well 102 and the P-type semiconductor substrate 101 is reverse-biased, such junction is depleted because of the bias effect, forming an internal capacitor in the device
Data Source
AI summary
A high voltage device is formed in a semiconductor substrate, and includes: a first deep well, a lateral lightly doped region, a high voltage well, an isolation region, a body region, a gate, a source, a drain, and a first isolation well. The first deep well and the first isolation well are for electrical isolating the high voltage device from neighboring devices below a top surface of the semiconductor substrate. The lateral lightly doped region is located between the first deep well and the high voltage well in a vertical direction, and the lateral lightly doped region contacts the first deep well and the high voltage well. The lateral lightly doped region is for reducing an inner capacitance of the high voltage device when the high voltage device operates, to improve transient response.