Thin Film Pyroelectric Detector Research Articles

Effects of the Multilayer Structure on the Responsivity of Pyroelectric Thin Film Detectors

AbstractPyroelectric thin film detectors have advantages of wavelength independent sensitivity, room temperature operation and direct incorporation with integrated circuit amplifiers. Pyroelectric thin films with good quality have be prepared by many advanced thin film technologies [1-2]. The responsivity of pyroelectric thin film detectors is dependent on the thermal properties of the substrate, on which pyroelectric thin film detectors are prepared. The heat conduction in the detectors was investigated using the one-dimensional heat flow equation and the expressions describing the detectors performance were derived for pyroelectric thin films detectors with multilayer structure. The numerical simulation showed that the pyroelectric thin film detectors need effective heat isolation. If the air gap could be the heat isolation layer, which is between the bottom electrode and substrate, the iesponsivity of detectors would be higher than that of detectors which have no heat isolation in certain modulation frequency range.

Thermophysical Measurements and Interfacial Adhesion Studies in Ultrathin Polymer Films Using Homodyne Photothermal Spectrometry

Homodyne laser photopyroelectric spectrometry (PPES) is a new photothermal detection scheme which uses electronic mixing to downshift a high-frequency swept wave photothermal response into a bandwidth of approximately one kilohertz. A rapid photopyroelectric impulse response is recovered from the downshifted component at high time resolution and is used, here, in two different geometries, to probe the thermal and interfacial properties of assemblies composed of submicron-thick-ness polymer films deposited on the metallized surface of a pyroelectric thin-film detector. In the thermal transmission mode geometry, the sample is excited by irradiation in a very thin opaque surface layer, and the transit time of a heat pulse through the sample to the pyroelectric transducer can be used to obtain a thickness or thermal diffusivity measurement. By the use of an inverse mode geometry, a metal/polymer interface is excited by irradiation of an optically transparent polymer thin-film sample attached to the metallized surface of the pyroelectric transducer. Heat flow at short distances from the bond interface can be monitored by the pyroelectric effect through the high time resolution of the homo-dyne photopyroelectric measurement. The combination of information obtained in these two geometries with an analysis of the thermal wave reflections which occur at interfaces between materials of dissimilar thermal effusivity can be used to evaluate relative interfacial adhesion between the metal and polymer layer.

TfC16. Growth of perovksite PLZT thin films by dual ion beam sputtering

Abstract PLZT thin films have been deposited using the emerging PVD technique of dual ion-beam sputtering (DIBS). The DIBS process produces high quality orientated perovskite films of bulk refractive index, good stoichiometry and full density, i.e., few pinholes. Films have been formed at 500–600°C onto sapphire, fused silica, Mg0 and silicon substrates by sputtering from an adjustable composite PLZT ceramic/Ti and Pb metallic target. Some substrates were coated with platinum prior to deposition to allow longitudinal electrical measurements on the films. Perovskite lead titanate PLZT (0/0/100), PLZT (10/0/100) and PLZT (28/0/100) films have been grown, the former two are of interest for thin film pyroelectric detectors whereas the latter is a quadratic electro-optic suited to optical waveguide, shutter and switching applications.

Impulse Photopyroelectric Depth Profiling of Multilayers. Part II: Experiments with Amplitude- and Phase-Modulated Wideband Spectrometry

Impulse response photopyroelectric effect spectrometry (PPES) was implemented with the use of wideband excitation for the recovery of depth profiles of optical absorption in a series of multilayered thin-film polymer samples. The wideband PPES technique intensity modulates a cw laser beam with a waveform whose power spectrum is flat over the photothermal response bandwidth, enabling the recovery of the PPES impulse response (short pulse equivalent) by correlation and spectral analysis techniques. The impulse response measurement recovers a depth profile of subsurface optical absorption through the spatial dependence of the heat flux deposited in the sample by a short optical pulse. It shows excellent potential for use as a nondestructive evaluation tool in the analysis of polymers. The impulse response data recovered in this work could be accounted for by means of a theoretical model which neglected thermal reflections between the constituent sample layers. Absorption coefficient measurements on a single-layer sample were recovered through the time delay dependence of the PPES impulse response. The data were corrected for the effect of reflectivity at the thin-film pyroelectric detector surface, which significantly affects the time dependence of the impulse response. Several types of measurements were demonstrated on optically inhomogeneous samples. These included measurements of the thickness of transparent overlayers deposited on opaque substrates, depth-resolved spectroscopy, and techniques for improving multilayer contrast. The role of thermal wave reflections at the gas/solid interface was identified as a key factor in determining the depth profile contrast for subsurface spectral contributions, as well as the dependence of the impulse response on the thickness of nonabsorbing overlayers. Several approaches for optimizing photothermal depth profile contrast were demonstrated.

Photopyroelectric measurement of the thermal diffusivity of YBa2Cu3O7-xAND Bi2Sr2CaCu2Ox

Abstract Thermal diffusivity measurements for superconducting YBa2Cu3O7-x and Bi2Sr2CaCu2Ox are reported over the temperature range from 50 to 300 K. The results were obtained using frequency-modulated time-delay photopyroelectric spectrometry (FM-TDPS), which consists of chirped laster excitation of the sample and detection of the associated impulse by a thin-film pyroelectric detector.

Simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat by impulse-response photopyroelectric spectrometry

A novel photothermal technique is developed, which enables the simultaneous measurement of the thermal diffusivity α, thermal conductivity κ, and the specific heat C of a sample. The technique is based on frequency-modulated time-delay photopyroelectric spectrometry (FM-TDPS), which consists of chirped laser excitation of the sample and detection of the thermal impulse response by a thin-film pyroelectric detector. No calibration is required for the measurements; absolute values for α, κ, and C may be obtained without having to employ a reference sample. Results on superconducting YBa2Cu3O7−x are reported for the temperature range 50–300 K; the values obtained compare favorably with reported measurements of α, κ, and C for YBa2Cu3O7−x , which previously required separate experiments for their determination.

Photopyroelectric thin-film instrumentation and impulse-response detection. Part I: A theoretical model

Thin-film pyroelectric effect detectors provide a simple means of measuring thermal properties of solid samples. The present work reports a time-delay theoretical model of thin-film pyroelectric detection which enables the recovery of thermal diffusivity and thermal conductivity information from the impulse response of the pyroelectric system.

Thin-film pyroelectric detector made of an organic compound and used to measure parameters of pulsed laser radiation

An investigation was made of the main characteristics of pyroelectric detectors consisting of a thin oriented polycrystalline organic film, designed for response to pulses of 10–100 nsec duration and of ≥ 10−6 J energy in the wavelength range 0.266–16 μ. Prospects for the future use of such detectors are considered.

Temperature fluctuation noise in thin pyroelectric films

Abstract The method of calculating the temperature response of a thin film pyroelectric detector on a thick insulating substrate to incoming modulated radiation is used to calculate the corresponding temperature fluctuation noise spectrum. This spectrum is interesting in that it shows a 1/6 frequency dependence over a wide frequency range; apparently the heat diffusion process takes care of that. The calculated noise is usually masked by the temperature fluctuation noise due to fluctuations in the heat condition in the layer and its substrate.