Lateral BJT Layout With Base Under Gate for Compact Symmetry
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Solution Overview
Problem
The challenge in fabricating compact lateral Bipolar Junction Transistors (BJTs) is due to their larger natural area occupation, misalignment of N and P implants, and complexity in miniaturization processes such as self-alignment techniques and alignment with Shallow Trench Isolation (STI) and Resist Protection Oxide (RPO) processes.
Innovation Solution
The solution involves designing lateral BJTs with the base located underneath the gate, using symmetric layouts such as T, Pi, or H shaped gates to reduce gate and base resistances, and employing compact layouts with common base connections to minimize device size and mismatch sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional lateral BJT layout is used, then device functionality is achieved, but device area is large
Solution Approach 1:
The patent transitions from a conventional lateral layout to a vertical-under-gate layout where the base region is positioned underneath the gate structure. This dimensional reorganization allows the emitter and collector to be laterally adjacent while the base extends vertically underneath the gate, significantly reducing the device footprint while maintaining proper transistor functionality through controlled doping profiles.
2Manufacturing precision
If self-alignment techniques are used for miniaturization, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent employs preliminary doping actions where the base region is doped underneath the gate structure before final gate formation. This preliminary action establishes precise alignment boundaries that guide subsequent processing steps, eliminating the need for complex self-alignment techniques while maintaining high manufacturing precision through pre-defined doping profiles and mask patterns.
3Reliability
If symmetric layout is used, then variability is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent employs asymmetric doping profiles and asymmetric gate electrode configurations relative to the base region. The base is positioned underneath the gate with asymmetric extension on one side, and the emitter-collector spacing is deliberately asymmetric. This controlled asymmetry simplifies the manufacturing process by reducing alignment constraints while maintaining low variability through precise doping control and geometric optimization.
Data Source
AI summary
A lateral-bipolar junction transistor (BJT) including a semiconductor substrate, an insulator region disposed on the semiconductor substrate, and a well region comprising a well semiconductor of a first conductivity type disposed over the insulator region. An emitter region of a second conductivity type is disposed in the well region, and at least one collector region of a second conductivity type is disposed in the well region. A T shaped, Pi shaped or H shaped gate and gate oxide layer includes a gate portion extending between the emitter region and one or more collector regions, and a base is disposed underneath the gate portion. In other embodiments, a metal oxide semiconductor (MOS) transistor-based circuit similarly employs a compact Pi or H shaped gate and gate oxide layer.