MEMS Switch ESD Protection for IC Input Pads
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Solution Overview
Problem
Integrated circuits (ICs) face significant damage from electrostatic discharge (ESD) due to reduced gate-oxide thicknesses and pn-junction widths, leading to insufficient protection by existing parasitic diodes, which can result in damage even at lower voltages, and additional protection circuits increase the IC's cost and area.
Innovation Solution
A micro-electromechanical system (MEMS) switch with a 'normally grounded' configuration is used to protect transistors in interface circuits by electrically coupling input pads to ground or supply voltage, providing a low-resistance path for ESD discharge and reducing the area occupied compared to diode-based solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional protection circuits (diodes) are added around input pads to provide effective ESD protection, then ESD protection capability is improved, but device area and manufacturing cost significantly increase
Solution Approach 1:
The MEMS switch serves multiple functions: it acts as a protective element during ESD events by providing a low-impedance discharge path, and during normal operation it functions as a controllable switch for signal transmission. This multi-functionality eliminates the need for separate dedicated protection circuits, thereby reducing overall device area while maintaining robust ESD protection capability.
Solution Approach 2:
The invention exploits the voltage-dependent impedance characteristic of the MEMS switch. At normal operating voltages, the switch maintains high impedance to allow signal passage. During ESD events, when voltage exceeds the pull-in voltage, the switch transitions to low impedance state, automatically providing protection without requiring additional protection circuitry.
2Reliability
If additional protection circuits (diodes) are added around input pads to provide effective ESD protection, then ESD protection capability is improved, but manufacturing cost significantly increases
Solution Approach 1:
The MEMS switch serves multiple functions: it acts as a protective element during ESD events by providing a low-impedance discharge path, and during normal operation it functions as a controllable switch for signal transmission. This multi-functionality eliminates the need for separate dedicated protection circuits, thereby reducing overall device area while maintaining robust ESD protection capability.
Solution Approach 2:
The invention combines the ESD protection function with the normal signal transmission function into a single MEMS switch device. By merging these functions, the patent eliminates the need for separate protection diodes and their associated manufacturing processes, thereby reducing manufacturing complexity and cost while maintaining effective ESD protection.
3Manufacturing precision
If gate-oxide thicknesses and pn-junction widths are decreased to enable device scaling, then device density and integration are improved, but ESD protection capability deteriorates
Solution Approach 1:
The invention exploits the voltage-dependent impedance characteristic of the MEMS switch. At normal operating voltages, the switch maintains high impedance to allow signal passage. During ESD events, when voltage exceeds the pull-in voltage, the switch transitions to low impedance state, automatically providing protection without requiring additional protection circuitry.
Solution Approach 2:
The MEMS switch is pre-configured with a pull-in voltage threshold that is set below typical ESD event voltages but above normal operating voltages. This pre-setting creates a protective mechanism that automatically activates before damage can occur to the scaled transistors, cushioning them against ESD effects without requiring larger or more robust transistor designs.
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
The MEMS switch offers enhanced ESD protection with reduced area and cost, capable of withstanding higher ESD voltages and providing instantaneous discharge, improving the reliability of ICs by acting as a reversible, virtual shunt to ground.
Implementation Method 1
In the absence of a voltage applied to a control terminal of the MEMS switch, the MEMS switch is closed... When a voltage is applied to the control terminal of the MEMS switch, the MEMS switch is open
Data Source
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AI summary
Embodiments of an interface circuit are described. This interface circuit includes an input pad, a control node and a transistor, which has three terminals. A first terminal is electrically coupled to the input pad and a second terminal is electrically coupled to the control node. Moreover, the interface circuit includes a micro-electromechanical system (MEMS) switch, which is electrically coupled to the input pad and the control node, where the MEMS switch is in parallel with the transistor. In the absence of a voltage applied to a control terminal of the MEMS switch, the MEMS switch is closed, thereby electrically coupling the input pad and the control node. Furthermore, when the voltage is applied to the control terminal of the MEMS switch, the MEMS switch is open, thereby electrically decoupling the input pad and the control node.