A 200 x 256 Image Sensor Heterogeneously Integrating a 2D Nanomaterial-Based Photo-FET Array and CMOS Time-to-Digital Converters

The CMOS image sensor, which incorporates a silicon photodiode array and a signal processor on a chip, or in a multi-die stack, has become an indispensable part of our daily lives. While its dominance in digital image capture will foreseeably continue, research with future outlooks is actively searching for new optoelectronic devices, alternative to silicon photodiodes, to place on the CMOS signal processor. Two-dimensional (2D) semiconducting materials, in particular, atomically thin transition metal dichalcogenide (TMD) monolayers-which are one of the most actively researched solid-state materials-are especially promising candidates for these applications [1], [2]. The vision arises from the fact that TMD monolayer crystals of different chemical compositions exhibit different bandgaps, or different absorption wavelengths from infrared to visible, and that these atom-thick crystals with differing bandgaps can, in principle, be van der Waals stacked to produce diverse spectral sensitivities beyond what is possible with conventional CMOS image sensors. Despite this vision, however, TMD arrays, such as those made from
$\text{MoS}_{2}$
optoelectronic devices (photo-FETs), have been limited to 32 x 32 thus far [3], and have not been integrated on CMOS signal processing chips; graphene was integrated with CMOS electronics, but this semimetal uses additional layers, such as quantum dots, for light absorption [4].