Uncooled digital IRFPA-family with 17μm pixel-pitch based on amorphous silicon with massively parallel Sigma-Delta-ADC readout

Abstract

This paper presents the results of an advanced digital IRFPA-family developed by Fraunhofer IMS. The IRFPA-family compromises the two different optical resolutions VGA (640 x 480 pixel) and QVGA (320 x 240 pixel) by using a pincompatible detector board. The uncooled IRFPAs are designed for thermal imaging applications in the LWIR (8 .. 14µm) range with a full-frame frequency of 30 Hz and a high thermal sensitivity. The microbolometer with a pixel-pitch of 17µm consists of amorphous silicon as the sensing layer. By scaling and optimizing our previous microbolometer technology with a pixel-pitch of 25µm we enhance the thermal sensitivity of the microbolometer. The microbolometers are read out by a novel readout architecture which utilizes massively parallel on-chip Sigma-Delta-ADCs. This results in a direct digital conversion of the resistance change of the microbolometer induced by incident infrared radiation. To reduce production costs a chip-scale-package is used as vacuum package. This vacuum package consists of an IRtransparent window with an antireflection coating and a soldering frame which is fixed by a wafer-to-chip process directly on top of the CMOS-substrate. The chip-scale-package is placed onto a detector board by a chip-on-board technique. The IRFPAs are completely fabricated at Fraunhofer IMS on 8" CMOS wafers with an additional surface micromachining process. In this paper the architecture of the readout electronics, the packaging, and the electro-optical performance characterization are presented.

Capabilities of scaled microbolometers for uncooled thermal imaging below 10µm pixel pitch

“…The electro-optical performance of the nanotube-microbolometers is evaluated on Fraunhofer IMS's digital ROIC with 17 µm pixel pitch providing QVGA resolution. 10 In case of a pixel pitch of the nanotubemicrobolometer array of 8.5 µm and 6 µm, blind nanotube-microbolometers without electrical connection to the ROIC are placed periodically between the active nanotube-microbolometers with the latter featuring an electrical connection to the ROIC. Thus, a homogeneous pixel distribution over the whole array as well as a constant infrared absorption of each single pixel is ensured.…”

Low-Cost Microbolometer Type Infrared Detectors

“…Generally, the high-speed ADC with a high dynamic range is required for the utility in the CMOS microbolometer IRFPAs. Although the on-chip ADCs using the pixel-level Sigma-Delta (Σ-Δ) ADC [ 92 , 93 , 94 ], the monolithic pipeline ADC [ 95 , 96 ], and the column-parallel successive approximation register (SAR) ADC [ 97 ] are reported to be available to achieve the high sensitivity ROICs for microbolometer IRFPAs, there are no report about the on-chip ADC for readily available CMOS microbolometer IRFPAs. The CMOS microbolometer IRFPAs usually use external ADCs, due to the inadequate signal processing area in the monolithic FPA.…”

Preparation and Bolometric Responses of MoS2 Nanoflowers and Multi-Walled Carbon Nanotube Composite Network

“…Then, through electrical signal processing, the temperature of the target object is obtained. Nowadays, the main commercial uncooled thermistor materials are amorphous silicon (a-Si), vanadium oxide (VO 2 ), and germanium-siliconoxide [6][7][8]. However, a-Si shows long response times of tens to hundreds of ms [9,10].…”