Nb₅N₆microbolometer arrays for terahertz detection

Abstract

A novel room-temperature microbolometer array chip consisting of an Nb5N6 thin film microbridge and a dipole planar antenna, which is used as a terahertz (THz) detector, is described in this paper. Due to the high-temperature coefficient of the resistance of the Nb5N6 thin film, which is as high as −0.7% K−1, such an antenna-coupled microbolometer is ideal for detecting signals in a frequency range from 0.22 THz to 0.33 THz. The dc responsivity, calculated from the measured I–V curve of the Nb5N6 microbolometer, is about −760 V/W at a bias current of 0.19 mA. A typical noise voltage as low as 10 nV/Hz1/2 yields a low noise equivalent power (NEP) of 1.3 × 10−11 W/Hz1/2 at a modulation frequency above 4 kHz, and the best RF responsivity, characterized using an infrared device measuring method, is about 580 V/W, with the corresponding NEP being 1.7 × 10−11 W/Hz1/2. In order to further test the performance of the Nb5N6 microbolometer, we construct a quasi-optical type receiver by attaching it to a hyperhemispherical silicon lens, and the result is that the best responsivity of the receiver is up to 320 V/W. This work could offer another way to develop a large scale focal-plane array in silicon using simple techniques and at low cost.