Diagnostic Ring Oscillator Biasing for CMOS Aging Separation
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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 using metal gate/high-k dielectrics and conventional CMOS technologies with poly-Si gates and SiO2 or SiON gate dielectrics.
Innovation Solution
The development of a diagnostic ring oscillator (RO) circuit for DC and transient characterization, which includes a Design-For-Reliability (DFR) RO design optimized to enable dynamic and static aging, allowing for separate measurement of NBTI and CHC components through a DFR RO circuit with enhanced enable circuits and external static bias options, and the use of a dedicated RO power supply for precise measurement.
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 accurate separation of NBTI and CHC components cannot be achieved due to measurement delay
Solution Approach 1:
The patent segments the RO circuit into multiple independent inverter stages with separate biasing control. This allows individual stages to be stressed with different voltages and durations, enabling separate measurement of NBTI and CHC effects by selectively activating specific stages during stress periods.
Solution Approach 2:
The patent implements dynamic biasing control where the RO circuit can switch between different operating modes (stress mode, measurement mode, recovery mode) with controllable timing. This dynamic control enables precise separation of aging mechanisms by adjusting stress duration and measurement timing to capture transient effects before they decay.
2Adaptability or versatility
If standard RO circuits are used, then frequency measurement can be obtained, but independent control of charge currents for separate NBTI and CHC measurement is not possible
Solution Approach 1:
The patent designs the RO circuit to serve multiple functions: it can operate as a standard oscillator for frequency measurement, as a stress application circuit for inducing aging, and as a measurement circuit for characterizing degradation. The same physical circuit structure supports all three functions through configurable biasing and control signals.
Solution Approach 2:
The patent incorporates preliminary action by pre-configuring the RO circuit with dedicated control terminals and biasing networks that prepare the circuit for specific measurement modes before actual stress or measurement occurs. This allows rapid switching between measurement types without reconfiguring the physical circuit.
Data Source
AI summary
Methods and apparatus for a diagnostic ring oscillator (RO) circuit for DC and transient characterization. The RO circuit includes a plurality of symmetrical stages coupled via a 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. 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 an enable stage configured to set the inverter chain 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 a feedback signal. The RO circuit can operate in multiple modes including an AC mode, a DC mode, and a hybrid mode.