Bidirectional Bipolar Transistors for Low Voltage Drop Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bidirectional power converters face inefficiencies due to diode drops and high on-state voltage drops in switching devices, particularly in power-packet-switching converters, which limit their ability to achieve high voltage resistance and bidirectional conduction with minimal losses.
Innovation Solution
The use of merged double-base bidirectional opposite-faced devices operating under high non-equilibrium carrier concentrations, with fully-symmetric double-base bipolar transistors that have emitter and base structures on both surfaces of a semiconductor wafer, allowing for low on-state voltage drops and high voltage resistance by actively managing carrier concentrations and conductivity modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional epitaxial base NPN transistor with N+ region over entire back surface is used, then manufacturing simplicity is maintained, but bidirectional electrical symmetry is prevented
Solution Approach 1:
The patent applies asymmetry in reverse - it creates a symmetric structure where conventional transistors are asymmetric. By forming emitter regions and base contact regions on both front and back surfaces of the semiconductor substrate, the device achieves bidirectional electrical symmetry, allowing identical electrical characteristics in both conduction directions while maintaining compatibility with conventional manufacturing processes
Solution Approach 2:
The patent segments the semiconductor device into distinct front and back surfaces, each with its own emitter and base contact regions. This segmentation allows independent optimization of each surface while achieving overall bidirectional symmetry, with each surface functioning as a complete transistor structure
2Loss of energy
If bipolar transistor is driven into high level non-equilibrium carrier densities, then voltage drop is reduced, but beta decreases
Solution Approach 1:
The patent changes the operating parameters by driving the bipolar transistor into high level non-equilibrium carrier densities, more than two orders of magnitude above intrinsic carrier density. This parameter change reduces the voltage drop to less than a Volt while accepting the trade-off of decreased beta, which is managed through the bidirectional switch configuration
Solution Approach 2:
The patent applies excessive carrier injection to achieve high level non-equilibrium conditions, intentionally over-driving the transistor beyond normal operating levels. This excessive action produces the desired low voltage drop effect, with the reduced beta compensated by the overall circuit configuration
3Reliability
If device is optimized to withstand high voltages, then voltage resistance is improved, but on-state voltage drop increases
Solution Approach 1:
The patent changes the carrier concentration parameter to high level non-equilibrium conditions, which fundamentally alters the device characteristics. This allows the device to simultaneously withstand high voltages (1200V or more) and achieve low on-state voltage drop (less than a Volt) by operating in a regime where voltage drop is decoupled from voltage resistance
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
This approach enables bidirectional switching with less than a diode drop in each direction, achieving high voltage resistance and low on-resistance, thereby improving the efficiency and ruggedness of power-packet-switching converters.
Implementation Method 1
Semiconductor statistics under high level non-equilibrium carrier densities can be quite different from low level carrier densities. Conventional recombination is generally less relevant with high level carrier density than in low level conditions.
Implementation Method 2
Carriers can often interact directly in high level conditions through Auger interactions. The beta (ratio of emitter current to base current) will therefore normally decrease as a bipolar transistor is driven into high level non-equilibrium carrier densities.
Implementation Method 3
The use of merged double-base bidirectional opposite-faced devices operating under high non-equilibrium carrier concentrations, with fully-symmetric double-base bipolar transistors that have emitter and base structures on both surfaces of a semiconductor wafer, allowing for low on-state voltage drops and high voltage resistance by actively managing carrier concentrations and conductivity modulation.
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Methods, systems, circuits, and devices for power-packet-switching power converters using bidirectional bipolar transistors (BTRANs) for switching. Four-terminal three-layer BTRANs provide substantially identical operation in either direction with forward voltages of less than a diode drop. BTRANs are fully symmetric merged double-base bidirectional bipolar opposite-faced devices which operate under conditions of high non-equilibrium carrier concentration, and which can have surprising synergies when used as bidirectional switches for power-packet-switching power converters. BTRANs are driven into a state of high carrier concentration, making the on-state voltage drop very low.