Bipolar Junction Transistor Stress Liner for RF Performance
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Solution Overview
Problem
Current bipolar junction transistor structures and fabrication methods lack improved designs that enhance carrier mobility and frequency performance for radiofrequency applications.
Innovation Solution
A bipolar junction transistor structure with a raised collector and emitter, featuring a stacked intrinsic and extrinsic base layer arrangement, and a stress liner positioned to overlap with the raised portions of the collector, emitter, and extrinsic base layer, which incorporates tensile or compressive strain to enhance carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bipolar junction transistor structure is used, then the device complexity is low, but the carrier mobility and frequency performance are insufficient for radiofrequency applications
Solution Approach 1:
The base region is segmented into two distinct layers: an intrinsic base layer and an extrinsic base layer. This segmentation allows the intrinsic base to provide a narrow width for high carrier mobility and frequency performance, while the extrinsic base provides doping for electrical contact and stability, thereby resolving the contradiction between performance and complexity
Solution Approach 2:
Different regions of the transistor are assigned different material compositions and doping characteristics. The intrinsic base layer has undoped or lightly-doped semiconductor material for high mobility, while the extrinsic base layer has heavily-doped material for electrical stability. This local differentiation optimizes each region's function to achieve overall performance improvement without excessive complexity
2Reliability
If the base width is reduced to improve carrier mobility, then the frequency performance improves, but the manufacturing precision requirements increase
Solution Approach 1:
By dividing the base into intrinsic and extrinsic layers, the narrow width requirement is confined to the intrinsic base layer only, which can be precisely controlled during epitaxial growth. The extrinsic base layer can be thicker and more tolerant to manufacturing variations, thus reducing overall precision requirements while maintaining high carrier mobility through the narrow intrinsic region
Solution Approach 2:
The invention changes the doping parameter across the base region, creating a gradient from undoped/lightly-doped in the intrinsic base to heavily-doped in the extrinsic base. This parameter change allows the intrinsic base to achieve narrow width for high mobility while the extrinsic base provides a buffer that relaxes manufacturing precision constraints
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 solution achieves improved carrier mobility, allowing for higher frequency performance (fT/fmax) in radiofrequency applications by providing a narrow base width and increased surface area for contact landing, particularly effective for NPN or PNP bipolar junction transistors.
Implementation Method 1
a stress liner positioned to overlap with the raised portion of the collector, the raised portion of the emitter, and the extrinsic base layer, which incorporates tensile or compressive strain to enhance carrier mobility
Data Source
AI summary
Structures for a bipolar junction transistor and methods of forming a structure for a bipolar junction transistor. The structure includes a collector having a raised portion, an emitter having a raised portion, and a base laterally arranged between the raised portion of the emitter and the raised portion of the collector. The base includes an intrinsic base layer and an extrinsic base layer stacked with the intrinsic base layer. The structure further includes a stress liner positioned to overlap with the raised portion of the collector, the raised portion of the emitter, and the extrinsic base layer.