FDSOI Charge Pump Back-Gate Biasing for Threshold Voltage Reduction
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Solution Overview
Problem
In typical bulk CMOS processes, the high threshold voltage of transistor diodes results in lower maximum output voltage and lower voltage conversion efficiency due to the back-gate effect, limiting the performance of switched-capacitor charge pumps.
Innovation Solution
The use of a fully depleted silicon on insulator (FDSOI) structure or independent multi-gate devices to reduce the threshold voltage of transistor diodes during the charging and pumping phase, and dynamically biasing the back-gate to minimize on-state resistance and enhance voltage conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If bulk CMOS process is used with grounded bulk, then manufacturing is simplified, but threshold voltage increases due to back-gate effect
Solution Approach 1:
The patent transitions from bulk CMOS to FDSOI technology, moving from a three-dimensional bulk structure to a four-dimensional structure with an additional buried oxide layer. This dimensional change isolates the active channel from the substrate, eliminating the back-gate effect while maintaining manufacturing feasibility through established FDSOI fabrication processes
Solution Approach 2:
The patent dynamically changes the threshold voltage parameter by applying adjustable back-gate bias voltages to the FDSOI transistors. During the charging phase, a negative back-gate bias reduces the threshold voltage to minimize conduction losses, while during the holding phase, the bias is adjusted to restore the threshold voltage to predetermined levels, optimizing performance across different operational states
2Object-affected harmful factors
If threshold voltage of transistor diode increases, then back-gate effect is present, but maximum output voltage and voltage conversion efficiency decrease
Solution Approach 1:
The patent implements dynamic threshold voltage control by adjusting the back-gate bias voltage of FDSOI transistors based on the operational phase. During the charging and pumping phase, the back-gate bias is optimized to reduce threshold voltage and minimize on-state resistance, thereby reducing conduction losses and improving voltage conversion efficiency. This dynamic adjustment eliminates the static high threshold voltage problem caused by the back-gate effect in bulk CMOS
Solution Approach 2:
The patent changes the electrical parameters of the transistor diodes by applying controlled back-gate biases to FDSOI devices. This parameter modification allows the threshold voltage to be reduced during critical charging operations, directly improving voltage conversion efficiency by minimizing energy losses while maintaining the ability to restore parameters during holding phases
3Loss of energy
If back-gate bias is applied to reduce threshold voltage, then voltage conversion efficiency improves, but device complexity increases
Solution Approach 1:
The charge pump circuit generates its own back-gate bias voltages internally through integrated voltage generation circuitry, eliminating the need for external bias voltage sources. The system self-regulates by using its operational phases to naturally produce the required back-gate biases, reducing external complexity while maintaining the efficiency benefits of dynamic threshold voltage control
Solution Approach 2:
The FDSOI transistor structure serves multiple functions simultaneously: it acts as the main switching element, provides the back-gate effect control interface, and enables dynamic threshold voltage adjustment all within a single device architecture. This multi-functionality reduces overall system complexity compared to adding separate control circuits for each function
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 boosts the performance of charge-pump voltage generators by increasing maximum output voltage and improving voltage conversion efficiency, while saving power and avoiding limitations of forward biasing and latch-up.
Implementation Method 1
the threshold voltage of the transistor diode in a typical bulk CMOS process is high due to the back-gate effect
Implementation Method 2
use a fully-depleted silicon on insulator (FDSOI) structure to reduce a threshold voltage of a plurality of transistor diodes
Data Source
AI summary
The present disclosure relates to a structure which includes a diode-based Dickson charge pump which is configured to use an independent multi-gate device to reduce a threshold voltage of a plurality of transistor diodes during a charging and pumping phase.