Volkmar Norkus

Low-temperature PECVD-deposited silicon nitride thin films for sensor applications

Abstract Polymer-like silicon-rich SiN x :H films suitable for transparent VIS/NIR/MIR-range optical coatings were deposited by PECVD at a substrate temperature of 80 and 150°C. Optical properties and film microstructure were investigated by transmission/reflection measurements and by FTIR. Air exposure for more than 1 year reveals no post-oxidation with time. The application as an antireflective coating for IR-sensor arrays is demonstrated.

Infrared Responsivity of Pyroelectric Detectors With Nanostructured NiCr Thin-Film Absorber

This letter reports on the performance of LiTaO3- based pyroelectric single-element detectors coated with a nanostructured thin-film absorber consisting of the same material as the sensor electrodes (NiCr). The fabrication of the absorber structure is achieved with a thermal evaporation technique in high vacuum. A major benefit is the one-step deposition and the functional integration of the sensors top electrode and the absorption layer enabled by a technologically simple deposition technique. The NiCr absorber shows a very high absorption efficiency comparable to that of metal-black coatings but with considerably higher mechanical robustness. The relative spectral responsivity of the detectors was evaluated in the 1-15 μm wavelength range showing good uniformity for a film thickness of about 1 μm.

Process Technologies for High-Resolution Infrared Detectors Based on LiTaO3

IR system designers increasingly demand pyroelectric detectors demonstrating on the one hand a geometry and number of responsive elements, which are highly user- specific, and a very high signal-to-noise ration on the other. This paper describes the principal design of high- resolution single-element detectors and arrays based on the pyroelectric material lithium tentalate together with subtechnologies for manufacturing. It is shown that the production of self-supporting responsive elements with a thickness smaller than 5 micrometers will be feasible by applying a combined chemical and mechanical polishing together with ion beam etching. In the attempt to increase the absorption coefficient of these elements special silver black coatings are deposited, which result in an absorption coefficient (alpha) >= 0.92 in the wave range pitches of 50 micrometers were reached for ultrasonic bonding processes. Selected detector parameters are used to prove the potential advancement of detector characteristics, which will be feasible by applying these technologies.

Reactive ion beam etching of lithium tantalate and its application for pyroelectric infrared detectors

Abstract The properties of reactive ion beam etching (RIBE) of single crystalline lithium tantalate (LiTaO 3 ) and photoresist are reported, with particular attention given to the dependence on the gas flow, the ion beam current, the accelerating voltage as well as the angle of incidence. For the experiments a filamentless r.f. ion beam source and gas mixtures containing C 2 F 6 , CF 4 , Ar and O 2 were applied. Compared with Ar ion beam etching (IBE) the LiTaO 3 /photoresist etch rate selectivity was found to be three times higher. High selective RIBE of LiTaO 3 and photoresist is an efficient process for the production of one- and two-dimensional pyroelectric IR detectors: The thickness of a LiTaO 3 wafer patterned with photoresist must be reduced by etching by about 10–15 μm.

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.

Performance improvements for pyroelectric infrared detectors

The paper describes the newest layouts and the basic properties of pyroelectric single-element detectors and linear arrays with up to 512 responsive elements which are built on the basis of lithium tantalate. The research aimed to develop detectors with a signal-to-noise ratio that is as high as possible thereby ensuring optimum adjustment of the detectors to their planned application. Typical applications can be found in pyrometry, gas analysis, spectrometry and security technique. It is shown that special technologies (e. g., ion beam etching, absorption layers) are used to manufacture responsive elements for detectors with very high signal-to-noise ratios. For example, a specific detectivity D* (500 K; 10Hz; 1 Hz; τW=1) ≥ 1.5 x 109 cmHz1/2W-1 has been obtained for single-element detectors with a responsive area of [2x2] mm2. The measured peak value of the NEP for a linear array with 256 responsive elements was smaller than 0.5 nW (128 Hz). Moreover, the acceleration responsivity (disturbance variable) of the examined detectors was fundamentally reduced (factor 5) thanks to the application of new chip and detector layouts.

High-resolution pyroelectric linear arrays based on LiTaO3

Lithium tantalate (LiTaO3) is a material that is excellently suited for pyroelectric infrared detectors. Its figures of merit are first rate, it has a good long-time stability and it is available at reasonable cost. Researchers at the Institute for Solid State Electronics have been developing a flexible technology to manufacture LiTaO3 detectors for the last twelve years. As a result, devices can be produced that can be optimally adjusted to the planned application. This paper describes the design and basic features of linear arrays with up to 256 responsive elements. The arrays are hybrid devices consisting of the pyroelectric chip and a CMOS multiplexer. It is demonstrated that special patterning technologies (ion beam etching) and optical functional layers on the responsive element considerably increase the thermal and spatial resolution. Thus, NEP values smaller than 0.2 nW were obtained at 40 Hz chopper frequency. Main applications of detectors are the contactless temperature measurement and -- increasingly -- the spectrometry in the wavelength range 0.8 ... 25 μm.

Pyroelectric infrared arrays and their applications

For different applications the use of uncooled thermal infrared detectors is often a low-cost alternative to the cooled semiconductor detectors. By the development of a large number of novel detector technologies the thermal and spatial resolution ofthe thermal detectors could be improved considerably. On the basis of the pyroelectric material lithium tantalate (LiTaO3) a cheap and flexible detector technology was developed for the design and manufacturing of user-specific arrays even at small batch quantities. The possibilities of this technology are described by the example of newly developed linear arrays with 128 responsive elements of different sizes (pitch 100 i.tm) and 256 responsive elements (pitch 50 jtm) as well as a two-dimensional array with 16 x 8 responsive elements. The given detector properties ofthe arrays clearly show that the achieved detector properties meet the demands of many applications. Responsive elements having a thickness of less than 5 jtm can be produced by the use of ion-beam etching for the stmcturing ofthe pyroelectric chips. In connection with a low-noise CMOS read-out circuit, NEP-values lower than 1 .5 nW were obtained by it at a chopping frequency of 128 Hz. The effective capacity of the detectors is illustrated on the basis of two detector applications in devices for the twodimensional temperature measurement and in a spectrometer. Keywords: infrared, uncooled detector, pyroelectric, array, manufacturing, properties, thermal imaging, spectrometer

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.