Semiconductor Off-State Current Measurement via Capacitor Charge Integration
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Solution Overview
Problem
Current methods for measuring extremely low off-state currents in semiconductor devices, such as those with oxide semiconductor transistors, are inadequate, particularly for transistors with channel widths smaller than 70 nm, as they struggle to accurately quantify currents below 1×10−20 A over extended periods.
Innovation Solution
A current measurement method involving a capacitor and a transistor under test, where a charge is written to a capacitor through the transistor, then turned off, allowing data on potential versus time to be generated and fitted to determine parameters for calculating the off-state current using specific formulas, enabling precise measurement of extremely low currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current measurement methods are used, then measurement simplicity is maintained, but measurement precision deteriorates for currents below 1×10−20 A
Solution Approach 1:
The patent introduces a capacitor as an intermediary element to convert the measurement of extremely low current into the measurement of voltage change over time. The capacitor accumulates charge from the transistor's off-state current, and the resulting voltage change across the capacitor is measured instead of the current directly. This mediation allows precise measurement of currents below 1×10−20 A using standard voltage measurement equipment, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The patent replaces direct electrical current measurement with a voltage-time measurement approach. Instead of using complex current measurement equipment capable of detecting extremely low currents, the system uses voltage measurement across a capacitor and temporal analysis to infer the off-state current. This substitution of measurement methodology achieves high precision without requiring specialized high-precision current measurement instruments.
2Measurement precision
If measurement time is extended to capture low current behavior, then measurement precision improves, but loss of time increases
Solution Approach 1:
The patent performs preliminary charge accumulation in the capacitor during a controlled time period before measurement. By pre-charging the capacitor with the off-state current and then measuring the voltage change over a shorter subsequent period, the system achieves accurate current measurement without requiring extended measurement times. The preliminary charge storage action enables the use of shorter measurement intervals while maintaining precision.
Solution Approach 2:
The patent employs periodic measurement cycles where the transistor is alternately turned on and off, and the capacitor is periodically charged and measured. This periodic action allows multiple measurements to be taken over time, with each measurement requiring only a short time interval. The cumulative data from periodic measurements provides precise off-state current characterization without requiring any single measurement to span an extended period.
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 method effectively measures and calculates off-state currents down to 1×10−20 A, providing accurate long-term charge retention characteristics for semiconductor devices, particularly suitable for memory elements and devices with low off-state currents.
Implementation Method 1
a first terminal of a capacitor is electrically connected to a second terminal of the transistor; in the second step, the transistor under test is turned off to make the first terminal of the capacitor electrically floating
Data Source
AI summary
A semiconductor device in which a transistor has the characteristic of low off-state current is provided. The transistor comprises an oxide semiconductor layer having a channel region whose channel width is smaller than 70 nm. A temporal change in off-state current of the transistor over time can be represented by Formula (a2). In Formula (a2), IOFF represents the off-state current, t represents time during which the transistor is off, α and τ are constants, β is a constant that satisfies 0<β≤1, and CS is a constant that represents load capacitance of a source or a drain.IOFF(t)=CS×α×βτβ×tβ-1×e-(tτ)β(a2)