Series Cascode High-Voltage Switch With SOI Isolation
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Solution Overview
Problem
Traditional semiconductor processes are limited in switching voltages beyond the reverse voltage ratings of P-N junctions, making it difficult to achieve high voltage switching requirements for applications like micro-electromechanical systems (MEMS) that need voltages between 60 volts and 100 volts.
Innovation Solution
A high voltage semiconductor switch is formed using a chain of series coupled cascode circuits with clamp circuits to prevent overvoltage, which can be implemented on a silicon-on-insulator (SOI) wafer with a Silicon Dioxide or Sapphire insulator layer, allowing for switching between DC references.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional semiconductor processes with P-N junctions are used, then device integration is achieved, but voltage switching capability is limited to reverse voltage ratings of P-N junctions (20-30 volts)
Solution Approach 1:
The high voltage switch is divided into multiple cascode circuits connected in series, where each cascode circuit handles a portion of the total voltage. This segmentation allows the overall system to achieve high voltage capability (100V+) while each individual transistor operates within its safe voltage ratings, resolving the contradiction between integration and voltage capability.
Solution Approach 2:
The SOI insulator layer acts as an intermediary that electrically isolates devices on the same substrate, eliminating the P-N junction coupling constraint. This intermediary enables devices to be isolated from each other, allowing high voltage operation between devices without being limited by substrate P-N junction reverse breakdown voltages.
2Productivity
If multiple devices are formed using the device layer on a traditional wafer, then device integration is achieved, but voltage differences between devices are restricted by P-N junction reverse voltage ratings
Solution Approach 1:
The SOI insulator layer serves as a mediator that provides electrical isolation between devices formed on the same substrate. This isolation eliminates the harmful effect of P-N junction coupling, allowing each device to operate at high voltages independently without being constrained by the reverse voltage ratings of substrate P-N junctions.
3Reliability
If series coupled cascode circuits are used to achieve high voltage switching, then voltage handling capability is improved, but device complexity increases
Solution Approach 1:
Multiple cascode circuits are merged into a single integrated high voltage switch device structure. While individual cascode circuits are used to achieve the voltage division, they are combined and fabricated together on the same SOI substrate, sharing common control logic and physical space, thereby reducing overall system complexity compared to discrete implementations.
Data Source
AI summary
The present invention is a high voltage semiconductor switch that is formed from a chain of series coupled cascode circuits. In one embodiment, the switch may be a single-throw configuration coupled between an output and a direct current (DC) reference. In an alternate embodiment, the switch may be a double-throw configuration such that the output is switched between either a first DC reference or a second DC reference, such as ground. Each cascode circuit may have clamp circuits to prevent over voltage during switching transitions. The series coupled cascode circuits may be formed using discrete components or on a silicon-on-insulator (SOI) wafer, which may have a Silicon Dioxide insulator layer or a Sapphire insulator layer.