Atomic-layer-deposited zinc oxide as tunable uncooled infrared microbolometer material

ZnO is an attractive material for both electrical and optical applications due to its wide bandgap of 3.37eV and tunable electrical properties. Here, we investigate the application potential of atomic-layer-deposited ZnO in uncooled microbolometers. The temperature coefficient of resistance is observed to be as high as -10.4%K-1 near room temperature with the ZnO thin film grown at 120 degrees C. Spectral noise characteristics of thin films grown at various temperatures are also investigated and show that the 120 degrees C grown ZnO has a corner frequency of 2kHz. With its high TCR value and low electrical noise, atomic-layer-deposited (ALD) ZnO at 120 degrees C is shown to possess a great potential to be used as the active layer of uncooled microbolometers. The optical properties of the ALD-grown ZnO films in the infrared region are demonstrated to be tunable with growth temperature from near transparent to a strong absorber. We also show that ALD-grown ZnO can outperform commercially standard absorber materials and appears promising as a new structural material for microbolometer-based applications

A low-cost 128x128 uncooled infrared detector array in CMOS process

This paper discusses the implementation of a low-cost 128 x 128 uncooled infrared microbolometer detector array together with its integrated readout circuit (ROC) using a standard 0.35 mu m n-well CMOS and post-CMOS MEMS processes. The detector array can be created with simple bulk-micromachining processes after the CMOS fabrication, without the need for any complicated lithography or deposition steps. The array detectors are based on suspended p(+)-active/n-well diode microbolometers with a pixel size of 40 mu m x 40 mu m and a fill factor of 44%. The p(+)-active/n-well diode detector has a measured dc responsivity (R) of 4970 V/W and a thermal time constant of 36 ms at 50 mtorr vacuum level. The total measured rms noise of the diode type detector is 0.69 mu V for an 8 kHz bandwidth, resulting in a detectivity (D*) of 9.7 x 10(8) cm . Hz(1/2)/W. The array is scanned by an integrated 32-channel parallel ROC including low-noise differential preamplifiers with an electrical bandwidth of 8 kHz. The 128 x 128 focal plane array (FPA) has one row of infrared-blind reference detectors that reduces the effect of FPA fixed pattern noise and variations in the operating temperature relaxing the requirements for the temperature stabilization. Including the noise of the reference and array detectors together with the ROC noise, the fabricated 128 x 128 FPA has an expected noise equivalent temperature difference (NETD) value of 1 K for f/1 optics at 30 frames/s (fps) scanning rate. This NETD value can be decreased to 350 mK by improving the post-CMOS fabrication steps and increasing the number of readout channels

Single layer microbolometer detector pixel using ZnO material

This paper presents the development of a single layer microbolometer pixel fabricated using only ZnO material coated with atomic layer deposition. Due to the stress-free nature and high temperature coefficient of resistance of the ALD coated ZnO material, it can be used both as structural and active layers in microbolometer detectors. The design, simulations, and the fabrication optimization of 35. m single layer ZnO microbolometers are shown in this study. The designed pixel has a thermal conductance of 3.4x10(-7) W/K and a thermal time constant of 1.34 ms while it has a maximum displacement of 0.43 mu m under 1000g acceleration. This structure can be used to decrease the design complexities and fabrication costs and increase the yield of the detectors making them possible to be used in low-cost applications