Nb₅N₆ microbolometer array for terahertz detection

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, which is as high as -0.7% K^-1, of the Nb₅N₆ thin film, 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/Hz^1/2 yields a low noise equivalent power (NEP) of 1.3×10^-11 W/Hz^1/2 at a modulation frequency above 4 kHz, and the best RF responsivity, characterized using infrared device measuring method, is about 580 V/W, with the corresponding NEP being 1.7× 10^-11 W/Hz^1/2. In order to further test the performance of Nb₅N₆ microbolometer, we construct a quasi-optical type receiver by attaching it to the 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 with simple technique and low cost.