Bert Willing

Pyroelectric thin-film sensor array

Pyroelectric thin-film point detectors and 1 x 12 arrays have been fabricated and characterized. They consist of sol-gel-deposited PZT thin-film elements on micromachined Si3N4/SiO2 membranes. The measured current and voltage response as a function of modulation frequency of a 1 x 12 array element is compared with finite-element calculations. Voltage responsivities of almost 3000 V W-1 in vacuum and 800 V W-1 in air have been achieved for 0.4 mm x 0.9 mm elements. Some point detectors have been completely packaged and correct operation in a movement detection system has been demonstrated.

Piezoelectric cantilever microphone for photoacoustic GAS detector

Abstract New micromachined pressure sensors based on PZT coated silicon cantilevers have been fabricated and integrated in a photoacoustic gas detector. PZT Sol-gel thin films texture and composition were optimized with respect to the transverse piezoelectric coefficient e31,f. A best value of -12 C/m2 was obtained with (100)/(001) textured thin films at the MPB composition. Optimum stress compensation between the different layers composing the cantilever has been studied in order to yield flat cantilevers. A high response of 150 mV/Pa with a S/N of 700 at 1 Pa and 1 Hz bandwidth has been measured. The influence of the damping chamber under the cantilever is also reported.

Thin film pyroelectric array as a detector for an infrared gas spectrometer

We demonstrate the implementation of a thin film pyroelectric array as a detector in an infrared gas spectrometer. The 1 x 50 element array is integrated onto a silicon chip with a sol-gel deposited zirconium modified lead titanate film (PZT) as the pyroelectrically active layer and a submicron membrane for thermal insulation. The spectrometer fitted with this detector covers a spectral range of 1.6 mu m and is capable of simultaneously detecting 15 ppm of CO2 and 200 ppm CO. Limitations of the present setup stem from a not optimized thermal light source and the discrete readout electronics

Thin film pyroelectric arrays as infra-red detectors

Pyroelectric thin film 12-element linear arrays (element size 0.4x0.9 mm(2)) have been fabricated by standard photolithography techniques on silicon substrates. A voltage responsivity of almost 800 V/W in air and 3000 V/W in vacuum is measured at low frequencies (0.1-1 Hz). Measurements are compared to finite element simulations. Doping of lead titanate thin films have been studied. Incorporation of porosity and Ca-doping of lead titanate thin films was found to improve significantly the pyroelectric properties. 20% Ca doping increased p/epsilon to 3.3. Poling experiments with Zr doped lead titanate shows the necessity of high temperature poling to obtain high pyro-coefficients.

Spontaneous pyro- and piezoelectricity of sol-gel La-modified lead titanate thin films

Abstract Polycrystalline La-modified lead titanate thin films have been processed, by a diol-based sol-gel route, on Si-based substrates. Multiple deposition and crystallization steps were carried out in order to promote heterogeneous nucleation and, as a consequence, a preferred crystallographic orientation and self polarization. Crystallization was achieved by rapid thermal processing at 650°C for 50s, at a heating rate of ∼30°C/s. The films developed either a <111> or a mixed <100>/<001> preferred orientation, which were determined by quantitative texture analysis of X-ray pole figures. Hysteresis cycles of the piezoelectric d33 coefficient versus electric field were obtained by a double-beam laser interferometric technique and found to strongly depend on the film texture. <111> oriented films present a thickness-dependent spontaneous pyroelectric coefficient and field endurance of the piezoelectric coefficient. These films are thus, appropriate to be used in non-switching applications, such as pyroelectric infra-red detectors and integrated piezoelectric sensors.

Pyroelectric thin film sensor arrays integrated on silicon

Abstract Sol-gel deposited Pb(Ti,Zr)O3 thin films have been used to integrate pyroelectric arrays on silicon. The arrays of 1×12 (element size of 600 × 1100 mm2) and 1×50 elements (element size of 140 × 1100 mm2) are fabricated by standard photolithography techniques on top of a SiO2/Si3N4 buffer layer which acts as a thermally insulating membrane after micromachining of the silicon. The devices have been characterized using a large aperture blackbody radiation source operating at 423 K. Its radiation is focussed by an infrared optics onto a single element and provides a power density of 67 W/m2. A voltage responsivity of 460 V/W at a chopping frequency of 1 Hz is achieved. The frequency dependencies of the obtained current and voltage responsitivities allow to deduce the thermal and electrical time constants which are compared to thermal finite element calculations and the electrical circuit model.

Gas spectrometry based on pyroelectric thin-film arrays integrated on silicon

We report on a novel gas spectrometry technique using pyroelectric thin-him arrays. The 1 x 50 element arrays of PZT are integrated onto silicon using a membrane structure. The experimental characterization of the pyroelectric elements shows both high voltage and current responses in defined frequency ranges. Mounting the array as a detector in a commercial spectrometer, we demonstrate its capability of detecting the infrared absorption curves of gases by the example of CO2

Room temperature spectrometry in the MIR range

Simple solutions for spectra acquisition in the MIR range have been studied in order to develop analysis systems for various process control and safety applications. The detection unit is a 64-pixel linear detector (μray 64, IR Microsystems), based on pyroelectric thin film technology. This detector exhibits a high signal to noise ratio at room temperature and therefore is ideal for the production of rugged, low cost and simple to use mini-spectrometers. We combined various technologies, including dispersive optics (gratings) and linear variable filters (LVF), with the μray 64 detector to build small spectral engines. These devices have been tested and their characteristics will be discussed in terms of sensitivity, resolution and costs.

Infrared gas spectrometer based on a pyroelectric thin film array detector

We present a infrared gas spectrometer which is based on a pyroelectric thin film array showing a flat response from the visible to the far infrared. The integration of a monolithic linear detector array as a thin film onto silicon offers a low thermal time constant, and the spectrometer is capable of simultaneous detection of different gases without any moving part or cooling equipment. The resulting system yields a low cost solution for industrial and environmental monitoring applications.