Search

Linear detector array formats are suitable for applications where relative motion between the detector and scene provides an intrinsic scanning mechanism, such as industrial inspection systems and satellite-based earth and planetary observation. The linear array format facilitates the introduction readout features not available in 2-D formats and when combined with low cost packaging approaches reduces sensor cost. We present two linear uncooled detector arrays based on VO x microbolometer technology and integrated CMOS readout electronics. The IRL256B is a linear array of 256 detectors on a 52 μm pitch. It includes a parallel array of 256 reference detectors to provide coarse offset correction and substrate temperature drift compensation. The IRL512A consists of 3 parallel lines of 512 pixels on a 39 μm pitch. It is particularly well suited to multi-spectral pushbroom imaging applications. Each pixel includes active and reference detectors to reduce pixel offset, eliminate common mode power supply noise and increase immunity to chip temperature drift. All pixels are integrated in parallel and the data are output in 14-bit digital format on three parallel output buses. The microbolometer detector design can be customized for selected wavelength ranges from NIR to VLWIR. The IRL256B has been integrated in industrial thermal line-scan imagers and spectrometers and may also be employed in uncooled airborne imaging and scanned surveillance or inspection systems. The IRL512A has been selected as the baseline detector for a number of future earth observation satellite missions.

Modified thermal sensors have been produced and characterized for fingerprint recording applications. The sensors are derived from the IR imaging technology developed at INO. The sensor array is made of 160 x 120 pixel VO x based micro thermistors that provide an image of a surface area of 8.3 x 6.2 mm 2 with a resolution of 488 dpi. The sensors were reinforced to withstand the mechanical pressure of the finger and the electrical discharges from the human skin. It is shown that despite their low thermal insulation, the sensors provide an image of the fingerprint pattern with relatively high contrast and resolution. With the acquisition electronics of an IR imager, the temperature of the sensor must be controlled. Measurements of the thermistor temperature were performed in order to access the intrinsic properties of the fingerprint sensors. The NETD is on the order of 2 10 -3 °C when the pass band of the filter is 330 kHz. The temporal behavior of the thermistor temperature shows that 10 ms after the finger has been brought into contact with the sensor, the temperature difference between thermistors in ridge and valley areas of the fingerprint DT r,v may reach 80 10 -3 °C, for an initial temperature difference between the finger and the sensor of 1 °C. Once the sensor reaches a steady thermal state after a long time, the same difference decreases to 1.9 10 -3 °C. The required temperature difference DT r,v , estimated to be 4.8 10 -3 °C to achieve an adequate signal to noise ratio, is relatively easy to reach at short and at long time periods. A modification to the method of acquisition is proposed to cancel the effect of the thermal drift of the sensor and to eliminate the need for the sensor temperature stabilization with a TEC. With this method, the recording of the fingerprint pattern may be achieved in 50 ms after the finger has been brought into contact. This leads to interesting gains in space, time and power consumption. Finally, for applications where the finger must remain in contact with the sensor, the same method may be efficient to reduce the need for thermal control.

INO has been active in microbolometer and FPA technology development since the early 1990s. Microbolometer detectors based on VO2 films with TCR above 3% are typically fabricated. VOx films with TCR above 2% have been developed for applications where FPA temperature is not stabilized. INO is continuing its development of high fill factor pixels with sizes down to 25 micrometers and new macro- and micro-packaging technology. All fabrication is done on six inch wafers in INOs newly expanded clean room facility. INO currently offers as standard products 256x1 and 160x120 pixel FPAs with 52 micrometers pixel pitch. Both arrays have simple, robust, and versatile CMOS readout integrated circuits (ROICs) that may be accessed in self-scanning or random access mode, and reference detectors for on-chip coarse offset and temperature drift compensation. Single frame NETDs (f/1, 300 K, 8-12 micrometers ) are on the order of 150 - 250 mK and may be reduced by frame averaging. Prototyping boards have been developed for both arrays, and the 160x120 FPA has been integrated in a number of thermal cameras and instruments. In collaboration with its clients, INO has developed several FPAs for specific space and terrestrial applications. Custom ROICs fabricated in several different CMOS processes from multiple foundries have been used. A 512x3 pixel microbolometer FPA with 39 micrometers pitch is being developed for the European Space Agency. The array is designed for multi-spectral pushbroom imaging applications and features a novel ROIC with very low 1/f noise, pixel by pixel offset and drift compensation, variable integration time, and digital output. Its single frame NETD (f/1, 300 K, 8-12 micrometers ) is nominally 80 mK.

Prototypes of VO2-based bolometric detectors with lateral dimensions of 25 X 25, 30 X 30, 35 X 35, 40 X 40 and finally 50 X 50 micrometers2 and fill factors approaching 90% are presented. These detectors are grouped in hardwired linear arrays as large as 512 X 1 pixels. Under DC biasing, the fabricated detectors, even the smallest ones, exhibit responsivities from 48,000 to 120,000 VW-1, detectivities in the range of 1.5 X 108 cm Hz1/2W-1 and response times in the range of 5 ms. These new bolometric detector structures contain hidden-legs placed completely underneath the bolometer platform. Results of simulations of the mechanical, optical and electrical properties of these new detector structures are presented. A complete detector fabrication process flow is described.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Linear bolometer arrays are well suited to industrial and space applications, where the object or scene may be convenientlyscanned by a conveyor or in a push-broom mode. The linear format facilitates the introduction of readout features notgenerally available in two-dimensional arrays. Such features include pixel by pixel offset and temperature drift compensation,as well as pixel-level filtering. The latter permits the filtering of detector noise down to a narrow bandwidth while preservinga high output bandwidth to allow oversampling. The former permits superior temperature drift compensation since each pixelmay have a dedicated, matched temperature sensing element.Three types of linear and quasi-linear bolometric detector arrays are being developed at INO within the framework of anR&D program jointly financed by INO and the Centre for Research in Earth and space Technology (CRESTech) of NorthYork (Ontario). The prototypes of these arrays, namely the 1RL256A, 1RL256B and 1RL256C are described in this paper.