High Voltage Bipolar Transistor Bias Shield
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Solution Overview
Problem
Bipolar power transistors face a trade-off between collector-emitter breakdown voltage (BVCEO) and cut-off frequency (FT), with prior art structures experiencing high base-collector capacitance and long transit times due to the placement of collector contacts far from the emitter, leading to reduced switching speed and compatibility issues with high voltage applications.
Innovation Solution
A lateral BJT design with a bias shield positioned between the base and collector contacts, allowing dynamic control of collector-base breakdown properties by applying a bias voltage to create accumulation or depletion regions, thereby reducing base-collector capacitance and optimizing the BVCEO/FT trade-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If collector contacts are positioned far from the emitter to achieve higher breakdown voltage, then BVCEO is improved, but transit time increases and FT is reduced
Solution Approach 1:
A bias shield structure is introduced as an intermediary element positioned between the collector and base contacts. This bias shield acts as a mediator that modifies the electric field distribution in the collector-base depletion region, enabling independent control of breakdown voltage and capacitance without requiring increased physical separation between collector and emitter contacts.
Solution Approach 2:
The invention changes the electrical parameters of the collector-base junction by applying a bias voltage to the bias shield. This bias voltage dynamically adjusts the depletion region width and capacitance, allowing the device to achieve high breakdown voltage without the traditional penalty of increased transit time and reduced cut-off frequency.
2Strength
If the epitaxial region is made thicker to achieve higher voltages, then breakdown voltage is improved, but transit time distance increases and switching speed is reduced
Solution Approach 1:
Instead of increasing the physical thickness of the epitaxial region, the invention changes the electrical parameters by applying a bias voltage to the bias shield. This creates a controllable depletion region that provides high breakdown voltage without increasing the physical transit distance for carriers, thereby maintaining fast switching speeds.
3Adaptability or versatility
If multiple implant regions are used to achieve multiple breakdown voltages, then voltage control is improved, but device complexity and manufacturing compatibility are reduced
Solution Approach 1:
The bias shield structure serves multiple functions: it controls the collector-base breakdown voltage, reduces base-collector capacitance, and enables dynamic switching between different voltage modes. This single multi-functional structure replaces what would otherwise require multiple separate implant regions and complex device architectures.
Solution Approach 2:
The invention uses parameter changes (bias voltage applied to the shield) to achieve multiple breakdown voltage levels without creating multiple physical implant regions. By varying the bias voltage, the device can dynamically adjust its breakdown characteristics, providing versatility without increasing structural complexity or compromising manufacturing compatibility.
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 increases the cut-off frequency by reducing transit time and capacitance while enhancing breakdown voltage, enabling faster switching and improved high-voltage performance with dynamic control over BVCEO/FT characteristics.
Implementation Method 1
The gate or bias shield is used to provide a bias field to dynamically control the collector-base breakdown properties
Implementation Method 2
The FT may be increased by biasing said shield so as to form an accumulation region beneath the shield
Implementation Method 3
The BVCEO may be increased by biasing the shield so as to form a depletion region beneath the shield
Implementation Method 4
improving shielding between the base and collector contacts to reduce base-collector capacitance (Cbc)
Data Source
AI summary
In a SOI process, a high voltage BJT structure with BVCEO versus FT control is provided by including a bias shield over the laterally extending collector region and controlling the bias of the shield.