CCD image sensors that could be printed on flexible substrates
Their aptly titled paper “Organic Charge-Coupled Device” published in the ACS Photonics journal reveals a prototype based on a unique channel geometry with relatively high electron mobilities and very long carrier lifetimes.
Unlike conventional inorganic CCDs that attract minority carriers to depletion regions at the semiconductor–insulator interface, the electrodes of the n-type organic semiconductor shift register are negatively biased to manipulate charge via repulsive potential barriers that extend through the thin film semiconductor.
Here, a four-pixel proof-of-concept OCCD uses repulsive potentials to confine and spatially manipulate photo-generated and background charge packets, passing them between closely spaced metal–insulator-organic semiconductor capacitors (form a linear four-pixel shift register). The device was able to transfer photo-generated electron packets across a 1.78 cm long, linear, three-phase shift register before being read out, and the researchers extrapolate that a 500×500 pixel organic CCD could be read out on a millisecond time scale.
Although they sport a lower charge mobility than conventional CCDs, organic CCDs could prove to be simpler and more cost effective to manufacture in flexible, ultralight, and large area form factors. This could make such devices useful to simplify complex optical systems. What’s more, their low weight and low sensitivity to cosmic radiations would makes OCCDs particularly attractive for space applications.
The researchers also anticipate that OCCDs could function as an element in ultralight optical imaging systems when used with thin film Fresnel lenses or as lightweight memory devices. Additionally, stacked, semitransparent OCCDs with individual pixel triads absorbing in different spectral regions could have a nearly 100% pixel fill factor in each colour and generate colour images without colour filters, the paper concludes.
University of Michigan – https://umich.edu
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