MOSFET Back Bias Utilizing Inherent BJT for Drain Current
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Solution Overview
Problem
Conventional MOSFETs do not effectively utilize the inherent bipolar junction transistor (BJT) formed during manufacturing, leading to underperformance in on-state drain current, and require higher operating voltages for non-volatile memory cells.
Innovation Solution
A semiconductor device structure and method that utilizes the inherent BJT by applying specific voltages to the buried layer and gate to enhance on-state drain current while maintaining unchanged off-state drain current, allowing the device to function as either a MOSFET or a memory cell with reduced operating voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inherent BJT is utilized to enhance MOSFET performance, then on-state drain current is increased, but device complexity increases due to additional bias control requirements
Solution Approach 1:
The inherent BJT is activated automatically when the MOSFET is turned on, utilizing the natural flow of drain current to provide base current to the BJT. This self-service mechanism eliminates the need for external bias control circuits, as the BJT turns on and off automatically with the MOSFET operation, thereby increasing on-state current without adding control complexity
Solution Approach 2:
The patent changes the operational parameters of the device by applying specific voltages to the buried layer to control the activation of the inherent BJT. By adjusting the buried layer voltage, the BJT can be turned on during MOSFET conduction to boost drain current, while remaining off during MOSFET cutoff to maintain low leakage, thus resolving the contradiction between current enhancement and control complexity
2Device complexity
If conventional MOSFET operation is used, then device structure is simple, but on-state drain current is insufficient
Solution Approach 1:
The patent merges the MOSFET and BJT functionalities into a single device structure by utilizing the inherent BJT formed during MOSFET manufacturing. The source, channel, and drain of the MOSFET simultaneously form the emitter, base, and collector of the BJT, creating a combined device that leverages both MOSFET and BJT characteristics to achieve higher on-state current without requiring separate devices or complex interconnections
Solution Approach 2:
The patent converts the previously harmful or neutral effect of the inherent BJT (which was typically nullified in conventional MOSFETs) into a beneficial feature. By intentionally activating the inherent BJT through buried layer biasing, the device transforms what was considered a parasitic element into a current-boosting mechanism, thereby improving on-state drain current while maintaining the original simple MOSFET structure
3Reliability
If higher operating voltage is applied to memory cells, then stable states are achieved, but energy consumption increases
Solution Approach 1:
The patent changes the voltage distribution parameters by applying optimized bias voltages to the buried layer and gate terminal. This parameter optimization allows the memory cell to achieve stable states at lower overall operating voltages, reducing energy consumption while maintaining reliability through enhanced charge storage capability in the body region
4Productivity
If the inherent BJT is activated, then on-state current is enhanced, but off-state leakage current may increase
Solution Approach 1:
The patent implements dynamic control of the BJT activation state through time-varying buried layer bias. The BJT is activated only during the MOSFET on-state to enhance current, and deactivated during the off-state to minimize leakage. This dynamic switching behavior, controlled by the gate voltage and buried layer bias combination, resolves the contradiction by adapting the BJT state to the operational requirements at each moment
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 increases on-state drain current and reduces operating voltage requirements, enabling efficient operation as both a transistor and a memory cell with stable states, improving performance and energy efficiency.
Implementation Method 1
a bipolar junction transistor (BJT) formed by the source region, the body and the drain region, wherein the gate is configured to turn on the MOS transistor and turn off the lateral BJT
Implementation Method 2
the gate is configured to turn on the MOS transistor and turn off the lateral BJT, wherein the lateral BJT is configured to be in a blocked state when the MOS transistor is turned off
Data Source
AI summary
A semiconductor metal-oxide-semiconductor field effect transistor (MOSFET) transistor with increased on-state current obtained through intrinsic bipolar junction transistor (BJT) of MOSFET has been described. Methods of operating the MOS transistor are provided.