Active Pixel Concept Combined With Organic Photodiode for Imaging Devices

Abstract

The active pixel concept is a promising architecture for imaging systems. We report on the electrooptical characterization of a hybrid organic active pixel sensor (APS) where an organic photodiode is integrated on top of an amorphous silicon thin-film transistor circuitry, which drives the image sensor and performs the signal processing. The active pixel approach provides an on-pixel amplification of the signal with a charge gain of up to 10. A fill factor that is close to 100% is obtained by embedding all transistors underneath the organic photodetector. We show that, as compared with organic passive pixels, the organic APS shows a higher sensitivity, making the detection of smaller signals possible.

A hybrid CMOS-imager with a solution-processable polymer as photoactive layer

“…As photoactive layer, a bulk-heterojunction of P3HT:PCBM (poly(3-hexylthiophene): [6,6]-phenyl C61 butyric acid methylester), absorbing in the visible range of the spectrum, was chosen. Alternatively, also SQ was added for NIR-enhanced absorption.…”

“…In addition, the liquid state of the semiconductor allows a straightforward deposition on any kind of substrate, including flexible ones [2][3][4][5] and amorphous silicon thinfilm transistor circuitry 6,7 , as well as combination with inorganic materials, for example colloidal quantum dots as infrared absorbers 8 . In addition, various organic materials absorbing at different wavelengths can be integrated in the photodetector.…”

“…In addition, various organic materials absorbing at different wavelengths can be integrated in the photodetector. For the visible range of the spectrum, a bulk-heterojunction of PCBM:P3HT (poly(3-hexylthiophene): [6,6]-phenyl C61 butyric acid methylester) (refs 9, 10) can be employed for photodetection 11 or squaraine (SQ) 12 for a near-infrared (NIR)-enhanced absorption. High performance and low-cost polymer photodetectors can also be realized beyond the absorption edge of silicon at 1.1 mm competing with resource-limited and costly InGaAs photodiodes 13 .…”

“…Solution-processability is also the key to develop low-cost hybrid imaging technologies that combine certain advantages of organic materials with technically mature silicon technologies. In previous attempts, organic materials were integrated on activematrix backplanes with a-Si:H thin-film transistors [6][7][8] , creating hybrid organic devices like flexible image sensor arrays 7 . Owing to the large pixel size of a-Si:H-devices, which typically exceeds 100 mm (refs 6-8), they are commercially employed only in largearea applications like X-ray image sensors and (organic) displays, as active-matrix organic light-emitting diodes 14 .…”

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

“…Many of the advances in image sensor technology have relied on digital imaging, in particular the use of complementary metal-oxide semiconductor (CMOS) devices, which were developed in the 1990s by Fossum et al [ 6,7 ] Figure 1 shows that the forecasted market for CMOS image and facilitate their use in other applications. These include: (i) the image processing software; [14][15][16][17] (ii) the image sensor architecture and layout; [18][19][20][21][22] (iii) the individual pixel sensor arrangement (typically "passive" or "active"); [ 12,23 ] (iv) the integration of "smart functions" onto the image sensor chips; [ 24 ] (v) the design and arrangement of the color separation system; [25][26][27] or (vi) the use of a different photodetector material, e.g., amorphous Si/SiC heterostructures, [ 28 ] organic semiconductors, [29][30][31] quantum dots, [ 32 ] nanoribbons/nanofi lms, [ 33 ] or nanorods. [ 34 ] Importantly, the type of photodetector material and color separation system associated with the image sensor play a dominant role in defi ning the quality of the fi nal image since they determine the spectral sensitivity, linear dynamic range, color accuracy and resolution.…”