Diagnostic Ring Oscillator for CMOS Aging Characterization
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Solution Overview
Problem
Existing semiconductor device characterization methods struggle to accurately quantify aging phenomena such as Negative Bias Temperature Instability (NBTI) and Channel Hot Carrier (CHC) degradation in CMOS technologies, particularly in advanced technology nodes with metal gate/high-k dielectrics, due to challenges in decoupling these mechanisms and measuring their effects on various parameters.
Innovation Solution
The implementation of a diagnostic ring oscillator (RO) circuit optimized for DC-static and transient characterization, which includes a Design-For-Reliability (DFR) RO design that allows for dynamic and static aging studies by configuring the circuit into NBTI/nMOS NCS or PBTI/pMOS NCS stress modes, using external power-gating transistors and independent control terminals to measure device degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional RO circuits are used for aging characterization, then device degradation can be measured, but the ability to independently control charge currents and separate NBTI/CHC mechanisms is insufficient
Solution Approach 1:
The patent segments the RO circuit into multiple independent controllable stages, each with separate charge and discharge current paths. This allows independent control of upward and downward transition currents, enabling separate characterization of NBTI and CHC mechanisms that were previously coupled in conventional RO designs.
Solution Approach 2:
The patent introduces dynamic control capabilities through multiple voltage terminals (VDD1, VDD2, VSS1, VSS2) that can be independently adjusted during operation. This dynamic control allows the circuit to adapt charge/discharge currents in real-time, providing versatility for different aging characterization modes while maintaining operational flexibility.
2Measurement precision
If measurement delay is reduced to decouple NBTI and CHC aging mechanisms, then aging component separation improves, but the circuit complexity increases
Solution Approach 1:
The patent designs a universal RO circuit structure that can operate in multiple modes (NBTI characterization, CHC characterization, combined aging studies) through a single integrated design. The same circuit with configurable voltage terminals serves multiple characterization purposes, avoiding the need for separate dedicated circuits for each aging mechanism.
Solution Approach 2:
The patent utilizes parameter changes in voltage levels and measurement timing to achieve different characterization goals. By adjusting voltage parameters (VDD1, VDD2, VSS1, VSS2) and measurement delays, the same physical circuit can isolate and measure different aging mechanisms without structural modifications.
3Adaptability or versatility
If standard RO characterization methods are used, then device aging can be monitored, but the ability to perform both DC-static and transient characterization simultaneously is limited
Solution Approach 1:
The patent introduces intermediary control elements (additional voltage terminals, control switches) that mediate between the aging device and measurement instrumentation. These intermediaries enable simultaneous DC-static and transient measurements by providing separate controlled paths for different characterization types without interfering with each other.
Data Source
AI summary
Methods and apparatus for a diagnostic in situ ring oscillator (RO) circuit for DC and transient characterization. The RO circuit includes a plurality of symmetrical stages coupled via an RO feedback signal line and forming an inverter chain, where each stage includes a CMOS inverter comprising a pair of pMOS and nMOS transistors coupled between power-gating transistors respectively coupled to a positive voltage source and ground, wherein an output of a CMOS inverter for the stage is coupled to an input for the CMOS inverter of a next stage. The first stage is a configurable enable stage to enable the inverter chain to be set into a defined logic state, followed by multiple pre-stage-DUT stages. The output of the last stage is feed back to the input of the enable stage to form an RO feedback signal. The RO circuit can operate in multiple modes including an AC mode, a DC mode, and a hybrid mode.