Micromachined Room-Temperature Air-Suspended Ni/Cr Nanobolometer

This paper presents the influence of the surrounding air on air-suspended microbolometers and nanobolometers. If the air-suspended bolometer is long and thin due to a low sheet resistance, the thermal loss through the air can be comparable to that through the bolometer structure, and therefore, the surrounding air can greatly affect the bolometer performance. The thermal models with the surrounding air effect are newly developed and verified using finite-element method simulations, and it is seen that bolometers with widths μm are required so as to minimize the effect of the surrounding air. Ni/Cr microbolometers and nanobolometers with the sheet resistance of 5.3-5.6 Ω/sq. and widths of 2-0.6 μm are fabricated and tested at room temperature. As the bolometer resistance increases, the microbolometer (w_b=2 μm) responsivity saturates at 83 V/W (limited by the surrounding air), while that of the nanobolometer (w_b=0.6 μm) continuously increases up to 315 V/W. Also, the 3-dB cutoff frequency of the nanobolometer (65 kHz) is three times higher than that of the microbolometer. The measured nanobolometer noise equivalent power is 14 pW/ √Hz for w_b=0.6 μm, l_b=20 μm, and R_b=184 Ω, which is ~ 2× better than the previous state-of-the art. Application areas are in terahertz power measurements and room-temperature imaging systems.