Miniaturized Optoelectronic SPR Sensor Based on Integrated Planar Waveguide and MIM Hot-Electron Photodetector

There is an increasing interest in miniaturized surface plasmon resonance (SPR) sensors for portable biosensing. Toward this goal, removing the use of an external spectrometer is a fundamental step to miniaturize the Kretschmann SPR sensors. In this article, we have proposed a new architecture of the SPR sensor with an electrical response in which the integrated hot-electron photodetector replaces the traditional spectrometer. In this device, the metal–insulator–metal (MIM) junction and planar waveguide (PWG) are integrated together as a multilayer. The structure is excited by a broad-spectrum light-emitting diode (LED) in the near-IR region. The coupling between the surface plasmon polariton (SPP) mode of the MIM junction and the PWG mode leads to predominated photoabsorption in the top layer of the MIM junction within a selective narrowband of excitation bandwidth. The center wavelength of the absorption band is determined by the refractive index of the analyte. We demonstrate that based on the hot-electron injection in the MIM junction, the open-circuit voltage of the MIM junction in the proposed architecture is proportional to the refractive index of the analyte and this feature can replace the wavelength interrogation of the SPR sensors. We show that electrical sensitivity can be improved by introducing an indium tin oxide (ITO) layer as a hot-electron blocker above the bottom electrode of the MIM junction. The response of the proposed sensor is calculated in detail, and its optical sensitivity is estimated to be ~8000 nm/refractive index unit (RIU), which turns to an electrical sensitivity of 12.5 V/RIU in our device.