Helmut Budzier

PyI12: Pyroelectric single-element detectors and arrays based on modified TGS

Abstract Pyroelectric detectors based on modified triglycine sulphate are described. Single-element detectors reach D*(500 K, 10 Hz, 25 °C) values up to 2×109cm Hz1/2/W. Linear arrays (128 elements, 100 μm pitch) and two-dimensional arrays (128×128 elements, 50 μm pitch) with NEP (500 K, 40 Hz, 25 °C) values up to 1 nW (0.16 nW/ Hz1/2) and NEP (500 K, 10 Hz, 25 °C values of 0.4 nW respectively were also realized.

Modulation transfer function of pyroelectric linear arrays

Abstract Spatial resolution, described by the modulation transfer function (MTF), is very important for multidimensional infrared sensors. The sensor-MTF of a pyroelectric linear array is determined by the geometric, thermal and capacitive MTF. These are calculated in detail by the use of a pyroelectric linear array developed at Dresden University of Technology, Institute for Solid-state Electronics. The linear array has 128 pixels with a centre-to-centre spacing of 100 μm. Deuterated and l -alanine doped triglycine sulfate (DTGS:L-A) or lithium niobate (LiNbO 3 ) are used as pyroelectric materials. Finally, the theoretical results are substantiated by measurements.

Pyroelectric IR single-element detectors and arrays based on LiNbO3 and LiTaO3

Starting from a characterization of the used pyroelectric materials LiNbO3 and LiTaO3 the paper describes the hybrid arrangement and essential properties of realized single- element detectors and arrays. It shows that the design and the production technique of pyroelectric chips have a strong influence on the thermal and spatial resolution of the detectors. This technique includes both the thinning process and reticulation of the chips, for which ion beam milling as a universal method was optimized and used. Single-element detectors with extremely thin, self-supporting LiTaO3 chips (dp < 2 micrometers ) were produced. With a responsive element of 2 X 2 mm2 in area, they have a specific detectivity D* (500 K; 10 Hz; 25 degree(s)C) > 1 X 109 cmHz1/2W-1. Linear arrays with 128 responsive elements of 90 X 100 micrometers 2 element size, 100 micrometers pitch, integrated readout circuit, and coated germanium window have a noise equivalent power (NEP) (500 K; 40 Hz; 25 degree(s)C) of 4 nW. The modulation transfer function MTFS (40 Hz; 31 p/mm; 25 degree(s)C) is 0.15 for pyroelectric chips without isolating grooves and was increased up to 0.45 by means of ion- beam milling of 10 micrometers wide isolating grooves between the responsive elements. First results of two-dimensional arrays with 128 X 128 elements, of 50 micrometers pitch and integrated CCD-readout circuit are presented.

Construction, properties and application of pyroelectric single-element detectors and 128-element CCD linear arrays

Abstract Pyroelectric detectors based on LiNbO 3 and L-alanine doped triglycine sulfate (DTGS:L-A) are described. Single-element detectors with ion-beam milled pyroelectric chips have D * (500 K, 10 Hz, 25 °C) values of 6 × 10 8 and 2 × 10 9 cm √Hz/W respectively. 128-element CCD linear arrays with NEP (500 K, 40 Hz, 25 °C) values of 4 and 1 nW respectively were also realized.

Influence of nonideal chopper design on nonuniformity in uncooled pyroelectric staring array systems

Choppers are inevitable parts of thermal imager or radiometer systems based upon uncooled pyroelectric focal plane arrays, since pyroelectric detectors require the incident radiation to be modulated. In comparison with other chopper techniques such as oscillator or shutter choppers rotating circular disks are considered superior in both mechanical simplicity and electronic control. However, the use of rotating disks introduces two non-ideal circumstances affecting the systems operation quality. Two-dimensional arrays require a bended chopper edge to approximate an ideal straight edge traveling over the array. Since sampling is performed line- sequentially, a local shift in time occurs between the sampling instant and the change of the optical chopper phase within each line. Furthermore, the chopper can only be placed in front of the entrance window of a detector array and, therefore, modulates the incident radiation in the blurred region of the optical path. This flattens the ideal rectangular modulation shape one would obtain if the chopper were able to run in the focal plane. Both effects attenuate the sensor output signal. The article presents a model for designing optimum chopper disks for 2- D arrays in order to achieve minimal possible signal attenuation. The optimization procedure incorporates all interdependencies between chopper layout, array size, chopper position, and readout velocity. The model also considers the unavoidable distance of the chopper plane from the focal plane and provides a chopper performance prediction method where the varying signal attenuation is discussed as contribution to the arrays nonuniformity. Finally, a sample design is given, and measurements are presented.

Pyroelectric linear array IR detectors with CCD multiplexer

Responsive pyroelectric linear arrays are described. After a short representation of the principal detector function, the pyroelectric materials L-alanine doped triglycine sulfate (DTGS:L-A) and lithium niobate (LiNbO3) are characterized, and the system parts pyroelectric chip, CCD-multiplexer, and hybrid arrangement are described in detail. Finally, the measured properties responsivity, noise equivalent power, and modulation transfer function are summarized.

Infrared line cameras based on linear arrays for industrial temperature measurement

The PYROLINE/ MikroLine cameras provide continuous, non-contact measurement of linear temperature distributions. Operation in conjunction with the IR_LINE software provides data recording, real-time graphical analysis, process integration and camera-control capabilities. One system is based on pyroelectric line sensors with either 128 or 256 elements, operating at frame rates of 128 and 544 Hz respectively. Temperatures between 0 and 1300DGRC are measurable in four distinct spectral ranges; 8-14micrometers for low temperatures, 3-5micrometers for medium temperatures, 4.8-5.2micrometers for glass-temperature applications and 1.4-1.8micrometers for high temperatures. A newly developed IR-line camera (HRP 250) based upon a thermoelectrically cooled, 160-element, PbSe detector array operating in the 3 - 5 micrometers spectral range permits the thermal gradients of fast moving targets to be measured in the range 50 - 180 degree(s)C at a maximum frequency of 18kHz. This special system was used to measure temperature distributions on rotating tires at velocities of more than 300 km/h (190 mph). A modified version of this device was used for real-time measurement of disk-brake rotors under load. Another line camera consisting a 256 element InGaAs array was developed for the spectral range of 1.4 - 1.8 micrometers to detect impurities of polypropylene and polyethylene in raw cotton at frequencies of 2.5 - 5 kHz.

Microbolometer-based infrared camera for the 3-5 μm spectral range

Until now Microbolometer cameras have been operated only in the long-wave infrared range (LWIR). Since microbolometers are now available with broadband windows and acceptable absorption in the mid-wave infrared range (MWIR), they are becoming more and more interesting for the MWIR range. Primarily for industrial applications, this wavelength range offers many advantages, e.g., for the measuring of glass temperatures or for supervision of furnace rooms. To achieve a sufficiently high measuring accuracy, such crucial MWIR peculiarities like carbon dioxide absorption lines and water-vapor absorption must be known. Such problems can be avoided by usage of narrowband filters. Usually, they have to be adjusted to the particular measurement task. The newly developed camera system is based on a 320 x 240 pixels LWIR microbolometer camera system. The optical channel had to be adapted to the microbolometer. In addition, special correction and calibrating procedures were implemented for the MWIR. The camera system is suitable for stationary use in harsh industrial environments. The robust housing may be completed by integrating water-cooling and air purge for the lens system. The camera is equipped with two trigger inputs for the synchronization with the process to be measured.

Uncooled pyroelectric arrays for contactless temperature measurements

Uncooled pyroelectric arrays can be advantageously used for contactless measurements of one- and two-dimensional temperature fields. Satisfying values of noise equivalent power NEP, modulation transfer function MTF and long term stability of responsivity, respectively, are necessary for these applications. Linear pyroelectric arrays developed for those purposes are described. The pyroelectric chip based on lithium tantalate contains 128 sensitive elements (element size 90 X 100 micrometers 2 with 100 micrometers pitch). A CMOS read-out circuit (low noise preamplifiers, S&H-stages, analog switching structures with digital components, output-amplifier) is specially designed. Pyroelectric chip, read-out circuit, and a PTAT temperature sensor chip, respectively, are mounted in a metal hermetic package with 8...12 micrometers germanium window. Measured NEP values reach 5 nW at a chopping frequency of 128 Hz. The modulation transfer function MTF (128 Hz, 3 lp/mm) measured is typically 60%. Devices for the measurement of temperature distributions based on linear arrays described contain the uncooled array, infrared optics, chopper, control electronics, analog to digital converter, and a comfortable digital processing unit for multi point pattern correction, accumulation, digital filtering and so on. The measuring range of such PYROLINE systems reaches from 0...80 degree(s)C, 50...300 degree(s)C, 200...700 degree(s)C (1500 degree(s)C), respectively.

Improving the shutter-less compensation method for TEC-less microbolometer-based infrared cameras

Shutter-less infrared cameras based on microbolometer focal plane arrays (FPAs) are the most widely used cameras in thermography, in particular in the fields of handheld devices and small distributed sensors. For acceptable measurement uncertainty values the disturbing influences of changing thermal ambient conditions have to be treated corresponding to temperature measurements of the thermal conditions inside the camera. We propose a compensation approach based on calibration measurements where changing external conditions are simulated and all correction parameters are determined. This allows to process the raw infrared data and to consider all disturbing influences. The effects on the pixel responsivity and offset voltage are considered separately. The responsivity correction requires two different, alternating radiation sources. This paper presents the details of the compensation procedure and discusses relevant aspects to gain low temperature measurement uncertainty.