Multifinger Semiconductor Trigger Voltage Uniformity
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Solution Overview
Problem
In semiconductor circuitry, multifinger semiconductor devices often fail to turn on simultaneously due to differences in parasitic resistance values across fingers, limiting their current handling capacity during electrostatic discharge events, and existing solutions introduce additional resistance or require significant semiconductor area.
Innovation Solution
A semiconductor circuit with external current injection sources and tunable components to match and modulate the trigger voltage across multiple fingers, compensating for variations in parasitic resistance values, ensuring uniform turn-on without adding resistive components or increasing area significantly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple fingers of ESD protection MOSFET are distributed over chip area, then ESD protection coverage is improved, but uniform turn-on of all fingers cannot be achieved due to parasitic resistance variations
Solution Approach 1:
The patent applies local quality by providing each finger with an individual current injection source that can be independently controlled. This allows each finger to receive a tailored current injection amount based on its specific parasitic resistance characteristics, enabling uniform turn-on voltage across all fingers despite their different locations and parasitic resistances in the distributed chip layout.
Solution Approach 2:
The patent changes the electrical parameter (current injection amount) for each finger individually. By adjusting the current injection amount as a controllable parameter, the trigger voltage of each finger can be compensated to achieve uniformity. This parameter adjustment allows the system to overcome the non-uniform parasitic resistance caused by distributed finger placement.
2Manufacturing precision
If drain ballasting resistance is added to equalize trigger voltage, then trigger voltage uniformity is improved, but additional resistance increases area and on-resistance
Solution Approach 1:
The patent replaces the passive mechanical/drain ballasting resistance approach with an active current injection mechanism. Instead of adding physical resistive components to equalize voltages, the system uses controllable current sources to actively compensate for parasitic resistance differences, achieving the same uniformity goal without the area and on-resistance penalties of additional resistive elements.
Solution Approach 2:
Rather than changing the physical structure by adding resistance, the patent changes the operational parameter (current injection amount) to achieve trigger voltage uniformity. This parameter-based approach avoids the need for additional physical components that would increase area and complexity.
3Power
If multiple fingers are connected in parallel, then current handling capacity is improved, but non-simultaneous turn-on limits effective current capacity
Solution Approach 1:
The patent implements a feedback mechanism where the trigger voltage of each finger is monitored and compared against a reference. Based on this feedback, the control circuit adjusts the current injection amount for each finger to ensure they all reach their turn-on threshold simultaneously. This feedback control maximizes the effective current handling capacity by ensuring all parallel fingers contribute to the ESD protection event.
Solution Approach 2:
The patent applies preliminary action by pre-injecting current into each finger before the ESD event occurs. This preliminary current injection prepares each finger to turn on at the same moment when the ESD stress is applied, ensuring that all fingers are ready to handle current simultaneously rather than sequentially, thereby maximizing the effective current handling capacity.
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3
AI summary
An external current injection source (45A, 45B, 45D and 45E) is provided to individual fingers (40A-40E) of a multi-finger semiconductor device to provide the same trigger voltage across the multiple fingers. For example, the external injection current is supplied to the body of a MOSFET or the gate of a thyristor. The magnitude of the supplied current from each external current injection source (45 A, 45B, 45D and 45E) is adjusted so that each finger (40A-40E) has the same trigger voltage. The external current supply circuit may comprise diodes or an RC triggered MOSFET. The components of the external current supply circuit may be tuned to achieve a desired predetermined trigger voltage across all fingers of the multi-finger semiconductor device.