LDMOS Minority Carrier Shunt for Snapback Suppression
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Solution Overview
Problem
LDMOS transistors are prone to destructive snapback events due to the generation of minority carriers from impact ionization, which can activate parasitic bipolar transistors, leading to catastrophic failures, especially in high-power RF applications.
Innovation Solution
Incorporating a minority carrier shunt region fabricated via a heavier implant near the gate, positioned closer to the gate without extending under it, to collect and redirect minority carriers away from the base-emitter junction of the parasitic bipolar transistor, thereby preventing its activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high operating voltages are applied between source and drain electrodes to increase power handling capability, then power handling capability is improved, but minority carrier generation through impact ionization increases leading to snapback events
Solution Approach 1:
A shunt region is introduced as an intermediary structure between the channel region and source region. This shunt region provides an alternative path for minority carriers, preventing them from reaching the base-emitter junction of the parasitic bipolar transistor. The shunt region is positioned adjacent to the channel region and extends closer to the gate than conventional structures, effectively intercepting minority carriers before they can trigger snapback, thus enabling higher operating voltages without compromising reliability
2Reliability
If the shunt region is positioned closer to the gate to improve snapback suppression, then snapback suppression is improved, but device complexity increases
Solution Approach 1:
The shunt region is strategically positioned only in the critical area adjacent to the channel region where minority carrier accumulation occurs, rather than uniformly throughout the device. By extending the shunt region closer to the gate in this specific local area, the patent achieves enhanced snapback suppression precisely where needed, without unnecessarily increasing overall device complexity or affecting other device regions
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 shunt region enhances the ruggedness of LDMOS devices by suppressing snapback events without compromising DC or RF performance, enabling higher power handling, gain, and bandwidth capabilities while avoiding performance degradations.
Implementation Method 1
charge carriers drift through a drift space between a channel region and the drain electrode under the electric field arising from an operating voltage applied between the source and drain electrodes
Implementation Method 2
The high operating voltages between the source and drain electrodes of an LDMOS device may give rise to the generation of minority carriers through impact ionization
Data Source
AI summary
A device includes a semiconductor substrate, source and drain regions in the semiconductor substrate and having a first conductivity type, a gate structure supported by the semiconductor substrate between the source and drain regions, a first well region in the semiconductor substrate, having a second conductivity type, and in which a channel region is formed under the gate structure during operation, and a second well region adjacent the first well region, having the second conductivity type, and having a higher dopant concentration than the first well region, to establish a path to carry charge carriers of the second conductivity type away from a parasitic bipolar transistor involving a junction between the channel region and the source region.