US researchers develop flexible “electronic eye”

Citation

Bogue, R. (2009), "US researchers develop flexible “electronic eye”", Sensor Review, Vol. 29 No. 1. https://doi.org/10.1108/sr.2009.08729aaf.002

US researchers develop flexible “electronic eye”

Article Type: Mini features From: Sensor Review, Volume 29, Issue 1

The human eye is a remarkable imaging device with many attractive design features, notably a hemispherical detector geometry that allows a wide field of view and low aberration. However, this type of configuration is extremely difficult to achieve using established optoelectronics fabrication technologies, owing to the intrinsically planar nature of the patterning, deposition, etching, materials growth and doping methods used. Now, a research team from the University of Illinois Urbana-Champaign and Northwestern University have developed a unique hemispherical camera which in many ways mimics the human eye and may one day form the basis of a “bionic eye”.

The device is based on an array of single crystal silicon detectors and electronics which is integrated into a flexible mesh. To fabricate the camera (Figure 2) a thin rubber membrane is moulded into a hemisphere shape and stretched to form a flat “drumhead”. A focal plane array (FPA) and other electronics, created by conventional planar fabrication methods, are transferred from a silicon wafer onto the tensioned drumhead membrane. Once the tension is released the membrane retracts to its original shape, compressing the FPA and causing specially designed interconnects to delaminate from the rubber, forming arcs pinned on the ends by detector pixels. The array package is then transfer-printed to a matching hemispherical glass substrate and assembled with a lens and connected to external electronics (Figure 3). The final system has the size and shape of a human eye.

Figure 2 The electronic eye after integration with a transparent hemispherical cap and a single-component imaging lens

Figure 3 Schematic of the assembly steps

Although the target application is retinal implants, the technology might also find uses in future generations of digital cameras which presently operate by focusing light onto a flat silicon sensor containing an array of light-sensitive pixels. However, expanding the field of view leads to distortion around the edges but owing to the geometry of this new device, simulations and imaging studies suggests the hemispherical detector arrays offer a broader field of view, more uniform illumination and fewer aberrations than flat cameras with similar lenses, as well as more uniform focusing across the image. According to John Rogers, Professor of Materials Science and Engineering at Illinois, “Conformally wrapping surfaces with stretchable sheets of optoelectronics provides a practical route for integrating well-developed planar device technologies onto complex curvilinear objects.” He added “We can now, for the first time, move device design beyond the flatland constraints of conventional wafer-based systems.” Takao Someya from the University of Tokyo, who wrote a commentary on the original publication, argues that the technology “heralds the advent of new classes of imaging devices with wide-angle fields of view, low distortion and compact size”.

This research was first reported in a paper entitled “A hemispherical electronic eye camera based on compressible silicon optoelectronics” in the 7 August issue of the journal Nature (Vol. 454, pp. 748-53) and was funded by the US National Science Foundation and the Department of Energy.

For further information, please contact: Professor John A. Rogers, University of Illinois Urbana-Champaign, E-mail: jrogers@uiuc.edu

Rob Bogue