ESD Protection Structure with Adjustable Triggering

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Solution Overview

Problem

Existing protection structures for integrated circuits against electrostatic discharges, such as those using bipolar transistors and thyristors, suffer from poorly controlled trigger voltages and large silicon surface area requirements, leading to potential component damage and increased stray capacitances.

Innovation Solution

A protection structure incorporating a thyristor forward-connected between input/output pads and a high power supply rail, with a diode and resistor configuration that allows for adjustable triggering, and an overvoltage detection circuit to manage currents during electrostatic discharges, reducing silicon area usage and stray capacitances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bipolar transistors are used for protection structures, then overvoltage removal capability is provided, but trigger voltage control is poor and device dimensions must be large

Engineering Contradiction:

Improveovervoltage removal capabilityVSAvoidtrigger voltage control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent introduces a resistor as an intermediary element connected to the base of the bipolar transistor. This resistor mediates the triggering process by controlling the base current, thereby enabling precise control of the trigger voltage. The resistor acts as a mediator between the input signal and the transistor switching action, solving the poor trigger voltage control problem while maintaining the overvoltage removal capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the electrical parameters of the protection structure by introducing a resistor with specific resistance value. This parameter change allows control over the trigger voltage level, transforming the uncontrolled bipolar transistor into a controllable protection device. By adjusting the resistor value, the trigger voltage can be precisely set to protect against specific overvoltage conditions.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If bipolar transistors are used for protection structures, then overvoltage removal capability is provided, but silicon surface area and stray capacitances increase

Engineering Contradiction:

Improveovervoltage removal capabilityVSAvoidsilicon surface area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent applies partial action by using a resistor to provide only the necessary base current for triggering, rather than requiring the full bipolar transistor structure to handle the entire protection function. This partial approach (using resistor + controlled transistor switching) achieves the same protection effect with reduced device dimensions and lower stray capacitances compared to using large bipolar transistors alone.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If large dimensions are used for bipolar transistors to withstand power dissipation, then electrostatic discharge protection is improved, but silicon surface area increases

Engineering Contradiction:

Improveelectrostatic discharge protectionVSAvoidsilicon surface area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent applies preliminary action by using the resistor to pre-control the base current before the transistor switches on. This preliminary control allows the transistor to switch on at a controlled, lower current level, avoiding the need for large transistor dimensions to withstand high power dissipation from the start. The resistor performs the preliminary current limitation function, enabling smaller transistor sizes while maintaining ESD protection capability.

Inventive Principle:

Principle #10Preliminary action

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 configuration provides controlled overvoltage removal with smaller silicon area requirements and lower stray capacitances, effectively protecting integrated circuits from electrostatic discharges while minimizing the risk of component damage.

Implementation Method 1

In case of a negative overvoltage between a pad and the ground, the base-collector PN junction of transistor 5 associated with the concerned pad, forward biased, becomes conductive, and the overvoltage is removed.

Methodology Applied

Scientific EffectForward biasing:

Implementation Method 2

In case of a positive overvoltage between the pad and the ground, the base-collector junction of transistor 5, reverse biased, becomes conductive by avalanche effect, and the current flows towards the ground

Methodology Applied

Scientific EffectAvalanche effect: Avalanche Breakdown

Data Source

PatentUS8755156B2Structure of protection of an integrated circuit against electrostatic discharges

Publication Date: 2014.06.17 STMICROELECTRONICS (ROUSSET) SAS

AI summary

An integrated circuit protected against electrostatic discharges, including input/output pads and first and second power supply rails, and: a thyristor forward-connected between each input/output pad and the second rail, each thyristor including, between its anode gate and its anode, a resistor; between each thyristor and the first rail, a diode having its anode connected to the anode gate of the thyristor and having its cathode connected to the first rail via a resistor for adjusting the triggering; and a triggering device capable of conducting a current between the first and second rails when a positive overvoltage occurs between these rails.