Omnivision's patent application US20160276380 "Photosensitive capacitor pixel for image sensor" by Wu-zang Yang, Chia-ying Liu, Chih-wei Hsiung, Chun-yung Ai, Dyson H. Tai, and Dominic Massetti proposes a capacitor as a sensing element in the pixel:
"In one embodiment, photosensitive semiconductor material 231 includes amorphous polysilicon. Amorphous polysilicon generally blocks wavelengths greater than 650 nm. Using amorphous polysilicon as photosensitive semiconductor material 231 potentially allows for the elimination of an infrared filter above pixel 410 to reject light above the non-visible spectrum.
Photosensitive semiconductor material 231 generates an image signal in the form of photoelectrons in response to receiving image light 205. The photoelectrons flow to storage node 221 via electrode 235 (and via metal connect 236 in the illustrated embodiment). After an exposure duration (a.k.a. an “integration period”), image charge generated by the image signal in charge storage node 221 can be transferred to floating drain 223 and eventually readout by readout circuitry."