Composite LDMOS Transistor with Non-Uniform Threshold Voltage
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Solution Overview
Problem
Power MOS transistor devices, such as LDMOS, face thermal and electrical failures due to excessive heat and current stress, particularly at the center of the device, where heat is not efficiently dissipated, limiting their safe operating area and energy handling capabilities.
Innovation Solution
A composite LDMOS transistor structure is designed with a central transistor having a higher threshold voltage and a peripheral transistor with a lower threshold voltage, arranged to balance heat generation and dissipation, using halo dopant implantation to establish the higher threshold voltage and shared transistor structures without isolation regions, allowing for improved thermal management and energy handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large LDMOS device is used to handle high currents and voltages, then the energy handling capability is improved, but thermal failure occurs due to excessive heat at the device center
Solution Approach 1:
The patent applies local quality by creating a non-uniform threshold voltage distribution across the device area. The center region has a higher threshold voltage (Vth) than the peripheral regions, which are optimized for lower Vth. This is achieved through selective dopant implantation or threshold voltage adjustment in the center region. The result is that the center generates less heat during operation while the periphery maintains high current handling capability, effectively resolving the thermal management issue in large power devices.
2Reliability
If the threshold voltage is increased to reduce heat generation, then the thermal safe operating area is improved, but the on-resistance increases
Solution Approach 1:
The patent implements local quality by spatially differentiating the threshold voltage across the device. The center region employs a higher threshold voltage to minimize heat generation where thermal dissipation is difficult, while the peripheral regions maintain lower threshold voltage to preserve low on-resistance and high current conduction capability. This localized optimization allows the device to simultaneously achieve both thermal reliability and electrical efficiency.
3Temperature
If the device area is increased to improve heat dissipation, then the thermal management is improved, but the device area enlargement is undesirable
Solution Approach 1:
The patent applies local quality by creating a non-uniform threshold voltage distribution across the device area. The center region has a higher threshold voltage (Vth) than the peripheral regions, which are optimized for lower Vth. This is achieved through selective dopant implantation or threshold voltage adjustment in the center region. The result is that the center generates less heat during operation while the periphery maintains high current handling capability, effectively resolving the thermal management issue in large power devices.
Solution Approach 2:
The patent employs asymmetry by creating an asymmetric threshold voltage profile across the device area. Rather than using a uniform threshold voltage, the device has a higher Vth in the center and lower Vth at the periphery. This asymmetric design optimizes heat generation distribution to match the thermal conduction pathways, reducing overall heat load without requiring increased device area.
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 composite structure enhances the thermal safe operating area, increases energy capability, and prevents thermal failure by distributing heat dissipation effectively, while maintaining low on-resistance and breakdown voltage levels, thus enabling the device to handle higher energy stresses without significant area enlargement.
Implementation Method 1
The first transistor includes a non-uniform channel such that the first transistor has a higher threshold voltage level than the second transistor
Data Source
AI summary
A device includes a semiconductor substrate, a first constituent transistor including a first plurality of transistor structures in the semiconductor substrate connected in parallel with one another, and a second constituent transistor including a second plurality of transistor structures in the semiconductor substrate connected in parallel with one another. The first and second constituent transistors are disposed laterally adjacent to one another and connected in parallel with one another. Each transistor structure of the first plurality of transistor structures includes a non-uniform channel such that the first constituent transistor has a higher threshold voltage level than the second constituent transistor.