Oxide Semiconductor Power MISFET High Voltage Design
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Solution Overview
Problem
Conventional power MISFETs using silicon semiconductors face challenges in achieving high withstand voltage with low on-state resistance, particularly at voltages above 1 kV, and struggle with high frequency characteristics, while oxide semiconductor-based MISFETs lack techniques for uniform donor distribution and p-channel region formation.
Innovation Solution
A power MISFET design utilizing a first and second oxide semiconductor layer with specific insulating layers and electrode configurations, allowing for low on-state resistance and high withstand voltage without the need for doping, using an i-type semiconductor with controlled carrier concentration and oxygen vacancy/hydrogen levels, and employing a unique electrode structure for efficient carrier injection and depletion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a drift region is provided in a silicon-based power MISFET to achieve high withstand voltage, then the breakdown voltage increases, but the on-state resistance increases significantly
Solution Approach 1:
The patent changes the semiconductor material parameter from silicon to oxide semiconductor, which fundamentally alters the electrical characteristics. Oxide semiconductors enable achieving high withstand voltage without the need for a drift region, thereby maintaining low on-state resistance. This material parameter change resolves the contradiction by providing a different physical basis for voltage blocking capability.
Solution Approach 2:
The invention extracts and eliminates the drift region from the device structure by using oxide semiconductor material that inherently provides high breakdown voltage without requiring a separate drift region. This removal of the drift region directly reduces the on-state resistance while maintaining the withstand voltage capability.
2Reliability
If the donor concentration in the drift region is increased to reduce on-state resistance, then the conductivity improves, but the depletion capability at high voltage deteriorates
Solution Approach 1:
The patent changes the semiconductor material from silicon to oxide semiconductor, which fundamentally alters the relationship between donor concentration and electrical properties. In oxide semiconductors, the material inherently provides high breakdown voltage without requiring low donor concentration, thus resolving the contradiction between conductivity and voltage blocking capability.
3Strength
If a thick drift region is formed to achieve high withstand voltage, then the breakdown voltage increases, but the fabrication complexity and time increase
Solution Approach 1:
The invention extracts and eliminates the need for a thick drift region by using oxide semiconductor material that provides high breakdown voltage inherently. This eliminates the requirement for forming thick regions through multiple doping and annealing steps, thereby reducing fabrication complexity and time.
4Strength
If multiple doping steps are performed to form drift region and source/drain regions in silicon MISFET, then the voltage blocking and conduction regions are formed, but the manufacturing process complexity increases
Solution Approach 1:
The invention extracts and eliminates the need for multiple doping steps and drift region formation by using oxide semiconductor material that inherently provides the required electrical characteristics. This simplifies the manufacturing process significantly.
Solution Approach 2:
The oxide semiconductor layer serves multiple functions simultaneously: it provides high breakdown voltage, forms the active channel, and eliminates the need for separate drift region. This multi-functionality reduces the number of fabrication steps required.
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 design achieves a low on-state resistance of less than 5 Ωcm² at 3 kV with improved heat dissipation and reliability, simplifying the fabrication process and overcoming the limitations of silicon-based MISFETs in high voltage applications.
Implementation Method 1
a voltage is applied to the semiconductor via a gate electrode through an insulating film or a Schottky barrier so that the state of the semiconductor is controlled, whereby current flowing between the source electrode and the drain electrode is controlled
Implementation Method 2
these oxide semiconductor materials have a large band gap of 3 eV or more
Data Source
AI summary
A power MISFET using an oxide semiconductor is provided. A drain electrode and a gate electrode having a trapezoidal cross section are formed with a semiconductor layer provided therebetween, a semiconductor layer is formed on a side surface of the gate electrode, and a source electrode is in contact with the semiconductor layer at a portion which overlaps with the top of the gate electrode. Between the drain electrode and the source electrode of such a power MISFET, a power source of 500 V or more and a load are connected in series, and a control signal is input to the gate electrode. Other structures and operating methods are also disclosed.