  Graphene has emerged as an ultrafast optoelectronic material for on-chip
photodetector applications. The 2D nature of graphene enables its facile
integration with complementary metal-oxide semiconductor (CMOS)
microelectronics and silicon photonics, yet graphene absorbs only $\sim$2.3% of
light. Plasmonic metals can enhance the responsivity of graphene
photodetectors, but may result in CMOS-incompatible devices, depending on the
choice of metal. Here, we propose a plasmon-enhanced photothermoelectric
graphene detector using CMOS-compatible titanium nitride (TiN) on the
silicon-on-insulator (SOI) platform. The device performance is quantified by
its responsivity, operation speed, and noise equivalent power. Its bandwidth
exceeds 100$\,$GHz, and it exhibits a nearly flat photoresponse across the
telecom C-band. The photodetector responsivity is as high as 1.4$\,$A/W
(1.1$\,$A/W external) at an ultra-compact length of 3.5$\,\mu$m, which is the
most compact footprint reported for a graphene-based waveguide photodetector.
Furthermore, it operates at zero-bias, consumes zero energy, and has an
ultra-low intrinsic noise equivalent power
(NEP$\,$<$\,25\:\text{pW/}\sqrt{\text{Hz}}$)
