Sub-10-pW/Hz0.5 Uncooled Micro-Bolometer With a Vacuum Micro-Package

This paper presents a very low noise suspended micro-bolometer with an in-situ vacuum micro-package so as to prevent thermal loss to the surrounding area and minimize the thermal conductivity of the ambient. Bolometer thermal models with respect to vacuum pressure are developed and verified by finite-element method (FEM) simulations. It is found that with the vacuum micro-package, a micro-scale (and not a nano-scale) size bolometer can achieve a noise equivalent power (NEP) close to the theoretical limit. Vacuum packaged Ni micro-bolometers with a sheet resistance of 6.2-6.5 Q/sq, widths of 1.3 and 2.3 μm, and a micro-vacuum ambient of 1 torr are fabricated using advanced micro-machining techniques. The measured responsivity (RESP) of a room-temperature micro-bolometer with w
_b
= 1.3 μm is 922 V/W (β = 1.54 MQ/W) for R
_b
= 275 Ω and I
_b
= 0.6 mA. The measured best NEP is 7.2 pW/Hz
^0.5
at 3-kHz modulation frequency for w
_b
= 1.3 μm, l
_b
= 40 μm, and R
_b
= 230 Ω, and is the first demonstration resulting in <;10 pW/Hz
^0.5
performance among uncooled micro-bolometers without any nano-patterning methods. The application areas are in low-cost THz imaging systems and wideband THz detectors.