Adding a charge blocking layer at the anode of organic photodiodes suppresses the current when forward biased. This simple structure can substitute thin film transistors as a switch when scaled into an array. However, the mechanism of the structure is still unknown. Meanwhile we observe a slow turn on when reverse biased, this indicates small and large signal injection dominated by different recombination mechanisms. Here, we developed a numerical model simulating this three-layer structure and compared against experimental data to describe the carrier dynamics and elucidate the physics dominant in this switchable photodiode.
Flat lenses based on metasurfaces promise to shrink imaging systems. While volume of a flat lens is negligible, the light field must propagate through a sizeable volume of image space behind the lens to finally form an image. This constrains the opportunity to shrink imaging systems. We introduce a general metric the Volumetric Imaging Efficiency (VIE) and show it’s an effective tool to compare disparate lenses and technologies. We use the VIE to illustrate the trade space where flat lenses excel – short focal length, wide angle lenses. We quantify their performance against conventional bulk lenses and discuss challenges for scaling to longer focal lengths.
Curved image sensors offer a new degree of freedom in optical system design that promise low-cost, small-volume solutions for wide field-of-view imaging. Stretchable polymer backplanes can provide the high-density of interconnects and tolerate the large deformations needed to transform planar, wafer-based image sensors into shapes with large nonzero Gaussian curvature. Here we demonstrate a thermoformable backplane based on glycolated polyethylene terephthalate (PETg) that can be deformed to a 98° spherical cap with 0.5” radius. We introduce a process to integrate such backplanes with a CMOS image sensor and release the circuit from the wafer to form a monolithically integrated image sensor that can be thermoformed to the desired shape.
There are enormous optical advantages to use a curved image sensor in place of conventional flat focal plane arrays (FPA) because optical systems intrinsically want to focus to a curved focal surface. For this reason, biological imagers such as the human eye have evolved a curved image sensor (i.e. the retina) that enables use of a simple lens to achieve nearly diffraction-limited imaging over a wide FOV – all in a compact package. Today’s digital imagers sample the curved focal surface using a flat FPA resulting in field-curvature aberrations that impose stringent limitations on the imager’s FOV, F/#, resolution and image quality. Here, we introduce techniques to fabricate hemispherical focal plane arrays to enable the development of compact, wide FOV imaging systems. We have developed monolithically integratable flexible interconnects that can be integrated onto the backside of a planar, silicon FPA designed for hemispherical deformation. These interconnects provide: (1) backside signal routing between small regions of the FPA that were designed to be electrically isolated and (2) a flexible handle for the FPA before a through-wafer etch is performed to mechanically separate the electrically isolated regions of the FPA wafer. This process provides a fully interconnected, flexible FPA that can conform to a hemispherical surface for use in visible (all silicon) or infrared (hybrid) imagers.
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