Transistor Cell Layout With Selective Airgaps for Lower Parasitic Capacitance
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Solution Overview
Problem
In transistor devices with parallelly coupled transistor cells, parasitic capacitances between electrodes negatively impact radio frequency behavior, and while airgaps can reduce these capacitances, they increase the device's area requirement on a chip die or wafer.
Innovation Solution
The transistor device incorporates a plurality of transistor cells with load electrodes arranged in a specific pattern, where a first pitch between some pairs of load electrodes is smaller than a second pitch, and airgaps are provided only between the load electrodes of the second subset, thereby optimizing the reduction of parasitic capacitances without significantly increasing the device's area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If airgaps are provided between all adjacent load electrodes to reduce parasitic capacitances, then radio frequency behavior is improved, but the pitch between electrodes increases and the device area increases
Solution Approach 1:
The patent applies local quality by providing airgaps between adjacent load electrodes only in specific regions where parasitic capacitance has the most significant impact on radio frequency performance. Instead of uniformly distributing airgaps across all electrode pairs, the invention selectively places them in critical areas, thereby reducing parasitic capacitance where it matters most while minimizing the overall area increase. This localized approach allows optimization of radio frequency behavior without proportionally increasing the device footprint.
2Object-generated harmful factors
If airgaps are provided between adjacent load electrodes, then parasitic capacitances are reduced, but the pitch between electrodes increases
Solution Approach 1:
The invention applies local quality by selectively providing airgaps between adjacent load electrodes only in regions where parasitic capacitance significantly degrades performance. By concentrating airgaps in critical areas rather than distributing them uniformly, the patent reduces parasitic capacitance effectively while minimizing the overall pitch increase. This localized strategy allows the majority of electrode pairs to maintain smaller pitches, thereby reducing the net increase in device area.
3Ease of manufacture
If load electrodes are arranged with uniform spacing to simplify manufacturing, then manufacturing precision is improved, but parasitic capacitances cannot be optimized
Solution Approach 1:
The patent resolves this contradiction by maintaining uniform electrode spacing in most regions to preserve manufacturing simplicity, while introducing airgaps selectively in specific regions where parasitic capacitance optimization is critical. This hybrid approach allows the manufacturing process to benefit from uniform spacing patterns while still achieving parasitic capacitance reduction through localized airgap formation. The selective airgap placement can be integrated into existing manufacturing flows without requiring complete redesign of the electrode patterning process.
Data Source
Figure 1A~1B
Figure 2~3B
Figure 4~5
AI summary
A transistor device is provided comprising a plurality of transistor cells. Each transistor cell comprises two load electrodes (11, 12) and a control electrode (13), wherein the load electrodes (11, 12) of the transistor cells are arranged spaced apart from each other in a first direction. A first pitch (pitch a) between adjacent load electrodes (11, 12) of a first subset of pairs of the load electrodes (11, 12) is smaller than a second pitch (pitch b) between adjacent load electrodes (11, 12) of a second subset of pairs of the load electrodes (11, 12). Airgaps (15) are provided between adjacent load electrodes (11, 12) of the second subset of pairs.