Fine Grain Voltage Scaling Back Biasing
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Solution Overview
Problem
Advanced semiconductor process technologies below 65 nm face challenges with reverse back biasing (RBB) and forward back biasing (FBB) as they cause performance decreases and increased leakage in high threshold voltage (HVT) devices, limiting their application and requiring complex redesigns or increased overhead for isolation.
Innovation Solution
Fine grain voltage scaling of back biasing, where programmable negative charge pumps (NCPs) and voltage regulators are distributed across a common substrate to apply discrete offset voltage levels to HVT, standard threshold voltage (SVT), and low threshold voltage (LVT) devices, optimizing RBB and FBB to minimize performance impact while reducing leakage, by subdividing the substrate into regions based on device type population density and adjusting voltage differentials between adjacent devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If reverse back biasing (RBB) is applied to reduce leakage in HVT devices, then leakage reduction is achieved, but performance decreases significantly
Solution Approach 1:
The patent applies different back biasing strategies to different device types (HVT, SVT, LVT) based on their specific characteristics and locations. HVT devices receive RBB for leakage reduction, while LVT devices in performance-critical paths receive FBB or no back biasing to maintain speed, creating localized optimal conditions for each device category
Solution Approach 2:
The system dynamically adjusts back biasing conditions based on operational requirements, allowing switching between RBB and FBB modes, and adjusting bias levels in real-time to optimize the trade-off between leakage reduction and performance maintenance under different operating conditions
2Productivity
If LVT and SVT devices are isolated from HVT devices into separate substrate domains, then performance impact on HVT devices is reduced, but device complexity and overhead increase significantly
Solution Approach 1:
Instead of creating separate substrate domains, the patent applies localized back biasing control to specific device regions. Different biasing conditions are applied locally to HVT, SVT, and LVT devices within the same substrate, avoiding the need for complex physical isolation structures while still achieving device-type-specific optimization
Solution Approach 2:
The patent changes the electrical parameters (back bias voltage levels and types) applied to different device regions rather than changing the physical substrate structure. By adjusting bias voltage parameters independently for each device type, the system achieves isolation-like effects without the structural complexity of separate domains
3Loss of energy
If uniform level of RBB is applied to all device types, then leakage reduction is achieved across the substrate, but HVT device performance is significantly degraded
Solution Approach 1:
The patent implements spatially varying back biasing where the bias voltage magnitude and polarity are adjusted according to the local device type distribution. Regions with HVT devices receive lower or zero RBB to preserve performance, while regions with LVT/SVT devices receive higher RBB for maximum leakage reduction, creating a non-uniform but optimized biasing landscape
Solution Approach 2:
The substrate is segmented into different back biasing zones based on device type population density. Each zone is independently controlled with appropriate biasing parameters, allowing HVT-rich regions to be protected from excessive RBB while LVT/SVT-rich regions receive aggressive leakage reduction, effectively segmenting the biasing strategy by device characteristics
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 reduces leakage and power consumption while maintaining performance, particularly for LVT devices, and allows for dynamic switching between RBB and FBB based on operational modes, thereby optimizing power savings and performance across different device types.
Implementation Method 1
Reverse back biasing (RBB) generally involves driving a voltage differential between the bulk (or body) connection and source terminal of the device to increase its threshold voltage (VT)
Implementation Method 2
FBB involves driving a voltage differential between the bulk (or body) connection and source terminal of the device in the opposite direction of RBB relative to the supply voltages to decrease its threshold voltage (VT)
Data Source
AI summary
An integrated circuit including a substrate, multiple devices, and voltage control devices. The devices may include high threshold, low threshold, and standard threshold voltage devices. The devices and the voltage control devices are distributed across and coupled to the same substrate. Each voltage control device is configured to apply a back bias voltage at one of multiple discrete offset voltage levels. At least one voltage control device applies a first offset voltage level for back biasing high threshold voltage devices and at least one voltage control device applies a second offset voltage level for back biasing low threshold voltage devices. The selection of back biasing is based on relative population density of the different types of devices and varies across the substrate. Fine grain reverse back biasing reduces leakage current while reducing any performance decrease. Fine grain forward back biasing improves performance while reducing any leakage current increase.