MOSFET Gate Oxide Defect Detection Through MOS Capacitor Decay
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Solution Overview
Problem
Existing technologies struggle to detect latent defects in the gate oxide of MOSFETs, particularly in RF ICs, due to their large size and the swamping effect of standard leakage currents, making it challenging to identify tiny leakage currents from defects that can cause field failures.
Innovation Solution
A method and circuital arrangement that measures the discharge rate of a voltage across a MOS capacitor in the MOSFET transistor by connecting a biasing circuit, charging the capacitor, and measuring the voltage decay rate to detect defects, both in a test environment and in the field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard leakage current measurement methods are used, then measurement simplicity is maintained, but measurement precision deteriorates due to swamping effect of large leakage currents in large-size RF transistors
Solution Approach 1:
The patent applies preliminary action by charging the MOS capacitor to a predetermined voltage level before performing the leakage current measurement. This pre-charging step establishes a known initial state that enables subsequent voltage decay measurement to accurately reflect defect leakage current, overcoming the swamping effect in large RF transistors.
Solution Approach 2:
The patent replaces direct electrical current measurement with voltage decay rate measurement. Instead of measuring the tiny defect leakage current directly (which is swamped by larger standard leakage currents), the system measures the rate at which voltage decays across the capacitor, providing indirect but more precise defect detection.
2Reliability
If direct current measurement is used, then measurement process is simple, but detection capability deteriorates for latent defects with tiny leakage currents
Solution Approach 1:
The patent substitutes direct current measurement with voltage decay measurement. By measuring how quickly the capacitor voltage decays rather than measuring the tiny leakage current directly, the system achieves much higher sensitivity for detecting latent defects with minimal leakage currents.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the defect and the measurement system. The capacitor converts the tiny defect leakage current into a measurable voltage decay signal, acting as a mediator that amplifies the detectability of latent defects.
3Measurement precision
If voltage decay rate measurement is implemented, then defect detection precision is improved, but measurement time increases due to charging and discharge cycles
Solution Approach 1:
The patent applies partial action by charging the capacitor only to a predetermined voltage level sufficient for detection rather than to maximum possible voltage. This optimized charging level reduces the time required for both charging and subsequent voltage decay measurement while maintaining adequate detection precision.
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
Enables effective detection of both active and latent defects by measuring voltage decay rates, allowing for early identification of potential failures and preventing field failures in ICs.
Implementation Method 1
charging a metal gate-oxide-semiconductor (MOS) capacitor of the MOSFET transistor with the biasing circuit
Implementation Method 2
measuring a discharge rate of a voltage across the MOS capacitor; and based on the measured discharge rate, detecting an absence or a presence of the defect
Data Source
AI summary
Methods and devices to detect defects in gate oxides of MOSFETs are disclosed. The disclosed methods and devices rely upon current measurements or decay measurements of the voltages across MOS capacitors. The described devices can be implemented in the RF circuits with elements having stringent reliability requirements.