Lateral Bipolar Transistors for SOI ESD Protection
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Solution Overview
Problem
Integrated circuits with semiconductor-on-insulator (SOI) technology face challenges in electrostatic discharge (ESD) protection due to reduced MOSFET oxide and junction breakdown voltage, increased interconnect resistivity, and limitations of lateral SOI diode-based protection approaches, especially in high-current Charged Device Model (CDM) domains, where vertical and deep body ESD structures are infeasible.
Innovation Solution
The integration of lateral bipolar transistors on SOI structures, featuring a semiconductor layer overlying an insulator layer with a trench region and partial trench isolation, allowing for the formation of a base, emitter, and collector without additional layers or masks, and enabling integration into existing fabrication processes, providing effective ESD protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lateral SOI diode-based protection approach is used, then ESD protection is provided, but excessive voltage build-up occurs along the ESD path involving power buses, power-clamps, and diodes
Solution Approach 1:
The patent changes the fundamental operating parameters of the ESD protection mechanism by transitioning from diode-based protection to bipolar transistor-based protection. The bipolar transistor operates in saturation mode during ESD events, providing a low-impedance discharge path that significantly reduces voltage build-up compared to diode-based approaches. This parameter change enables effective ESD protection while maintaining lower voltage stress on power buses and interconnects.
2Reliability
If vertical and deep body ESD structures are implemented, then ESD protection is improved, but the buried oxide layer makes such structures infeasible
Solution Approach 1:
The patent inverts the conventional ESD protection approach by abandoning vertical and deep body structures that are incompatible with SOI technology. Instead, it implements lateral bipolar transistors that are specifically designed to function effectively within the constraints of the buried oxide layer. This inversion of the structural approach makes ESD protection feasible in SOI technology while maintaining manufacturing compatibility.
Solution Approach 2:
The patent transitions from vertical ESD structures to lateral ESD structures by implementing bipolar transistors with horizontal current flow paths. This dimensional change allows ESD protection to be achieved within the planar constraints imposed by the buried oxide layer, enabling effective protection without requiring deep vertical structures that would be incompatible with SOI fabrication.
3Productivity
If technology scaling is pursued, then device density is increased, but MOSFET oxide and junction breakdown voltage are reduced
Solution Approach 1:
The patent changes the protection mechanism parameters by utilizing bipolar transistor saturation characteristics rather than relying on MOSFET oxide breakdown or junction breakdown. The bipolar transistor's ability to operate in saturation mode provides a controlled low-impedance path during ESD events, achieving effective protection without requiring high breakdown voltages that would conflict with scaled device dimensions.
4Reliability
If lateral bipolar transistors are integrated on SOI structures, then ESD protection is enhanced, but additional layers or masks are required
Solution Approach 1:
The patent achieves universality by designing lateral bipolar transistors that can be integrated into existing SOI CMOS fabrication processes using standard process steps. The bipolar transistor structures serve multiple functions: they provide ESD protection while also being compatible with standard device fabrication, eliminating the need for dedicated ESD-only process modules and reducing overall device complexity.
Solution Approach 2:
The patent implements self-service by utilizing the gate structure that is already present in standard CMOS devices. The gate serves dual purposes: normal device operation and ESD protection activation. During ESD events, the existing gate structure automatically becomes part of the bipolar transistor operation without requiring additional gate-specific components or control circuitry, enabling the device to serve its own ESD protection needs.
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 solution enables efficient ESD protection for fully depleted and partially depleted SOI technologies, reducing the need for special layers or masks and allowing for integration into existing processes, thereby enhancing the capacitive budget and reducing voltage build-up along ESD paths.
Implementation Method 1
The gate structure prevents doping of the trench portion of the semiconductor layer, and the trench portion of the semiconductor layer forms a base
Implementation Method 2
This solution enables efficient ESD protection for fully depleted and partially depleted SOI technologies
Data Source
AI summary
Integrated circuits with lateral bipolar transistors and methods for fabricating the same are provided. An exemplary integrated circuit includes a semiconductor layer overlying an insulator layer. The semiconductor layer includes a first region having a first thickness and a trench region having a second thickness less than the first thickness. The integrated circuit further includes an isolation region formed over the trench region of the semiconductor layer. Also, the integrated circuit includes a lateral bipolar transistor including a base formed in the trench region of the semiconductor layer, an emitter, and a collector.