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Causality behind lack of sensitivity increase with larger membrane diameters

Determine whether the lower yield of intact artificially stacked double-layer CVD graphene membranes at larger diameters, and the resulting reduction in actual active membrane area, is responsible for the observed absence of a significant sensitivity increase with increasing membrane diameter in the piezoresistive graphene pressure sensors reported here.

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Background

The paper evaluates piezoresistive pressure sensors based on arrays of suspended artificially stacked double-layer CVD graphene membranes over closed cavities. Sensitivity was extracted across devices with membrane diameters from 3.4 µm to 12 µm.

Contrary to expectation, sensitivity did not significantly increase with membrane diameter. The authors hypothesize that lower yields of intact membranes at larger diameters may reduce the actual active area, potentially explaining the observation. Due to limited data controlling yield at fixed diameters, this causal link could not be established.

References

The devices showed no significant sensitivity increase with increasing membrane diameter, although this would be expected. A possible explanation may by the lower yield of intact membranes at larger diameters, leading to a smaller actual active area (i.e., the area covered with intact membranes per device, calculated as the product of the theoretical suspended membrane area relative to the total channel area, and the yield of intact membranes in the respective device). This, however, could neither be confirmed nor disproven due to the limited amount of data with varying yield for the same membrane diameter and sample.

— High-yield large-scale suspended graphene membranes over closed cavities for sensor applications (2408.16408 - Lukas et al., 29 Aug 2024) in Results, discussion of Figure 4d–e; pages 15–16