Vertically integrated pixel microbolometers for IR imaging using high-resistivity VOx

Uncooled IR bolometers form an integral part of thermal imaging cameras. Vanadium oxide material currently used for IR imaging has a resistivity between 0.1 and 1 ohm-cm and a temperature coefficient of resistance (TCR) between -1.4%K-1 to -2.4%K-1. Higher TCR materials are desired, however, such materials inevitably have higher resistivity and therefore higher electrical resistance in a lateral resistor configuration. A high resistance leads to an increase in the Johnson-Nyquist noise of the bias-induced current, thereby limiting the performance of bolometers using high resistivity material. In this work, we demonstrate high resistivity, high TCR VOx and propose the use of a vertically integrated resistor configuration an alternate pixel structure design with lower Johnson noise when compared with the conventional lateral pixel design. Biased Target Ion Beam Deposition was used to deposit high resistivity vanadium oxide thin-films (~85 nm thick). Electrical characterization of lateral resistor structures showed resistivities ranging from 2 ⨯ 103 ohm-cm to 2.1 ⨯ 104 ohm-cm, TCR varying from -2.6%K-1 to -5%K-1, Johnson noise (pixel resistance of 1.3GΩ) of 4.7 to 6μV/√Hz and 1/f noise (normalized Hooge’s parameter (α/n)) of 5 ⨯ 10-21 to 5 ⨯ 10-18 cm-3. In contrast, the through-film resistor structures showed significantly higher resistivities at 3 ⨯ 104 Ohm-cm to 1.55 ⨯ 105 Ohm-cm, TCR similar to lateral resistive structure between -2.6%K-1 to -5.1%K-1, immeasurably low Johnson noise (pixel resistance of 48KΩ) and normalized Hooge’s parameter ranging from to 5⨯10-21 to 1⨯10-18 cm-3. These results indicate the possible use of through-film resistors as an alternative to the conventional lateral-resistor design currently used in uncooled imaging microbolometers.