Figure Of Merit For Detectors Research Articles

Figure of Merit for Detectors Based on Laser-InducedThermoelectric Voltages in La1−xCaxMnO3 andYBa2Cu3O7−σ Thin Films

A figure of merit (FOM) Z = Up/τr, where Up is the peakvoltage, and τr is the rise time of the laser-inducedthermoelectric voltage (LITV) signal, is defined for photodetector basedon the LITV and the influence of the parameters on FOM is analysed basedon the time dependence of LITVs in La1−xCaxMnO3 (LCMO)and YBa2Cu3O7−σ (YBCO) thin films grown on vicinal-cutsubstrates. We find that the FOM increases as the photon penetrationdepth decreases, and linearly increases with the thermal diffusionconstant D. To achieve the highest FOM, the film thickness d has to becontrolled to an optimum value. We also find that the FOM is directlyproportional to the laser absorption coefficient α0, thelaser energy density per pulse E, the illuminated length of film l,sin(2α) [αis the vicinal-cut angle], the Seebeckcoefficient anisotropy (Sab−Sc), and is inverselyproportional to the mass density ρ and the specific heat c0.

Dielectric and Pyroelectric Properties of 〈111〉‐Oriented Fe‐Doped 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 Single Crystals

Fe‐doped 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 (PMN–0.38PT) single crystals were grown by a modified Bridgman technique. Two kinds of single crystals with different iron ion molar ratios, (i) 0.2 mol% and (ii) 1.0 mol%, were obtained. The effect of doping iron ions on the dielectric and pyroelectric properties of the 〈111〉‐oriented PMN–0.38PT single crystals was examined. The temperature of the permittivity maximum (Tm) exhibits no dispersion behavior and decreases with increasing doping concentration. The dielectric loss of the 0.2 mol% Fe‐doped PMN–0.38PT single crystal is much lower than that of the high dopant content crystal (1.0 mol%) and undoped crystal, which makes it possess excellent pyroelectric performance. By a dynamic method, the measured pyroelectric coefficient and detectivity figure of merit (FD) of 0.2 mol% Fe‐doped PMN–0.38PT single crystal are 439 μC/m2·K and 56.3 μPa−1/2, respectively, both better than those of widely used pyroelectric single crystal LiTaO3. The results imply that the single crystal is a promising candidate for infrared detectors and other pyroelectric applications. The mechanism of doping effect was also discussed based on the principles of crystal chemistry.

The effect of Fe substitution on pyroelectric properties of 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 single crystals

Fe-doped 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 (PMN–0.38PT) single crystals with two different dopant concentrations, 0.2 and 1.0mol%, were grown by a modified Bridgman technique. The effect of Fe substitution on dielectric and pyroelectric properties was examined. The dielectric constant of the 0.2mol% Fe-doped PMN–0.38PT single crystal was controlled successfully, indicating the possibility of tuning the dielectric properties by doping with a small concentration of iron ions. The mechanism of doping effect was also discussed based on the principles of crystal chemistry. The pyroelectric response of the single crystals was measured using a dynamic method from 20to50°C. Compared with the 1.0mol% Fe-doped single crystal, the 0.2mol% Fe-doped sample possesses the better pyroelectric properties. At room temperature, the pyroelectric coefficient and detectivity figure of merit (FD) for the 0.2mol% Fe-doped sample are 568μC∕m2K and 53μPa−1∕2, respectively, and they increase slightly with temperature increasing. These excellent pyroelectric properties as well as being able to produce large-size and high-quality single crystals make this kind of single crystal a promising candidate for high-performance infrared detectors and other pyroelectric applications.

Composition, dc bias and temperature dependence of pyroelectric properties of 〈1 1 1〉-oriented (1 − x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 crystals

The pyroelectric properties of 〈1 1 1〉-oriented (1 − x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 (PMN– xPT) crystals with x = 0.21, 0.26, 0.30 and 0.33 have been investigated. The pyroelectric coefficients were measured using a dynamic technique under various thermal and electrical conditions. The pyroelectric coefficients decrease with increasing PT content and dc bias, and nearly increase linearly with increasing temperature from 20 to 55 °C showing little thermal hysteresis. At room temperature, PMN–0.21PT crystal has the highest pyroelectric coefficient of 17.9 × 10 −4 C/m 2 K. However, the best pyroelectric performance can be achieved for PMN–0.26PT crystal, with the voltage responsivity and detectivity figures of merit F v and F d of about 0.11 m 2/C and 15.3 × 10 −5 Pa −1/2, respectively, over a wide range of frequency from 50 to 30 kHz. The results demonstrate that superior pyroelectric performance makes 〈1 1 1〉-oriented PMN– xPT crystals a promising candidate for room-temperature infrared detectors and thermal imagers.

The crystallization and electrical properties of lead-based ferroelectric thin films for uncooled pyroelectric infrared detector

Epitaxially grown and polycrystalline PT, PLT and PZT thin films with thickness from 1 to 2 μm have been prepared on Pt/Ti/SiO2/Si substrates by means of the modified sol–gel spin-coating technique. The ferroelectric thin films have good crystallization behavior, excellent dielectric and pyroelectric properties. The pyroelectric coefficients of PT and PLT thin films are 2.9×10−8 C/cm2 k and (3.37–5.25)×10−8 C/cm2 k, respectively. The figures of merit for voltage responsivity of PT and PLT thin films (F I ) are 0.60×10−10 Ccm/J and (0.79–1.13)×10−8 Ccm/J, respectively. The figures of merit for current responsivity of these films are 9.0×10−9 Ccm/J and (10.5–16.0)×10−9 Ccm/J, and the figures of merit for detectivity of these films are 0.74×10−8 Ccm/J and (0.79–1.13)×10−8 Ccm/J, respectively.

Reply to “Comment on ‘Figures of merit for detectors in digital radiography’ ” [Med. Phys.31, 2364-2365 (2004)

Reply to “Comment on ‘Figures of merit for detectors in digital radiography’ ” [Med. Phys.<b>31</b>, 2364-2365 (2004)

Leakage current and pyroelectric properties of compositionally graded (Pb,Ca)TiO3 films

Highly (100)-oriented, compositionally graded (Pb,Ca)TiO3 (PCT) thin films with a Ca content from 0 to 24 mol % on Pt/Ti/SiO2/Si substrates were prepared by a sol-gel process. The graded structure of the Au/PCT/Pt film capacitor showed a well-saturated hysteresis loop at an applied field of 500 kV/cm with remanent polarization (Pr), and coercive electric field (Ec) values of 9.35 μC/cm2 and 130 kV/cm, respectively. At 100 kHz, the dielectric constant and dielectric loss of the film were 129 and 0.024, respectively. The leakage current density of the graded PCT film was less than 1.0×10-7 A/cm2 over a voltage range from 0 to 4 V. The conduction current depended on the voltage polarity. At low electric field (110 and 180 kV/cm, respectively, for Pt and Au electrodes biased negatively), the Au/PCT and PCT/Pt interfaces form a Schottky barrier. At high electric field (>110 kV/cm), the Au electrode biased negatively shows space-charge-limited current (SCLC) behavior. The temperature dependencies of the pyroelectric coefficients of the graded PCT film were measured by a dynamic technique. From 20 to 82 °C, the pyroelectric coefficients of graded PCT film remain steady in the range 106 to 118 μC/m2 K. The detectivity figure of merit (FD) of the graded PCT film was 6.7×10-6 Pa-0.5.

Figures of merit for detectors in digital radiography. II. Finite number of secondaries and structured backgrounds.

The current paradigm for evaluating detectors in digital radiography relies on Fourier methods. Fourier methods rely on a shift-invariant and statistically stationary description of the imaging system. The theoretical justification for the use of Fourier methods is based on a uniform background fluence and an infinite detector. In practice, the background fluence is not uniform and detector size is finite. We study the effect of stochastic blurring and structured backgrounds on the correlation between Fourier-based figures of merit and Hotelling detectability. A stochastic model of the blurring leads to behavior similar to what is observed by adding electronic noise to the deterministic blurring model. Background structure does away with the shift invariance. Anatomical variation makes the covariance matrix of the data less amenable to Fourier methods by introducing long-range correlations. It is desirable to have figures of merit that can account for all the sources of variation, some of which are not stationary. For such cases, we show that the commonly used figures of merit based on the discrete Fourier transform can provide an inaccurate estimate of Hotelling detectability.

Figures of merit for detectors in digital radiography. I. Flat background and deterministic blurring.

Digital radiography systems can be thought of as continuous linear shift-invariant systems followed by sampling. This view, along with the large number of pixels used for flat-panel systems, has motivated much of the work which attempts to extend figures of merit developed for analog systems, in particular noise equivalent quanta (NEQ) and detective quantum efficiency (DQE). A more general approach looks at the system as a continuous-to-discrete mapping and evaluates the signal-to-noise ratio (SNR) completely from the discrete data. In this paper, we study the effect of presampling blur on these figures of merit for a simple model that assumes that the background fluence is constant and that the blurring of the signal is deterministic. We find that for small signals, even in this idealized model, commonly used DQE/NEQ formulations do not accurately track the behavior of the fully digital SNR. Using these NEQ-based figures of merit would lead to different design decisions than using the ideal SNR. This study is meant to bring attention to the assumptions implicitly made when using Fourier methods.

Pyroelectric properties of phosphoric acid-doped TGS single crystals

Pyroelectric properties of phosphoric acid (H3PO4)-doped triglycine sulfate (TGSP) single crystals grown from solutions containing 0.1–0.5 mol of H3PO4 have been studied. Incorporation of H3PO4 into the crystal lattice is found to induce an internal bias field (Eb) and is observed through the presence of a sustained polarization and pyroelectricity beyond the transition temperature. The internal bias field has been estimated theoretically by fitting the experimentally measured data on temperature dependence of the pyroelectric coefficient (λ), dielectric constant (ε′) and polarization (P). A high Eb value in the range 9 × 103–15.5 × 104 V m−1 is obtained for crystals grown with 0.1–0.5 mol of H3PO4 in the solution, and a specific concentration of 0.2–0.25 mol of H3PO4 in the solution during crystal growth is found to be optimum for a high figure of merit for detectivity, Fd = 428 µC m−2 K−1.

Preparation and Characterization of Ba1-xSrxTiO3 Based Thin Films for Pyroelectric Applications

ABSTRACTThe use of pyroelectric thin films in uncooled IR detectors has many advantages over the present IR detector technology, which requires extensive cooling for operation. These advantages include reduced weight, reduced footprint, reduced complexity, increased reliability, and decreased maintenance. Ba1-xSrxTiO3 (BST), based thin films are ideal candidates for use in these devices due to their tailorable materials properties. These properties include a high dielectric constant, low dielectric loss, high electrical resistivity, as well as a high pyroelectric constant. BST thin films were doped with Mg in varying amounts, from 0 to 20mol%. The thin films were deposited via metalorganic solution deposition (MOSD) on Pt/Ti/SiO2/Si substrates. Annealing temperatures ranged from 500 to 750 °C. The films were characterized for structural, microstructural, compositional, surface morphological, dielectric and insulating properties. Glancing angle x-ray diffraction (GAXRD) was used to determine crystallinity, phase formation and film orientation. Field emission scanning electron microscopy (FESEM) and cross sectional transmission electron microscopy (TEM) were employed to access surface morphology and microstructure. The Materials Detectivity Figure of Merit (FOM), D*, [D*=pi/(CV(ε0εrtanδ)1/2] was used to evaluate the film's detectivity response. Our results show that undoped Ba60Sr40TiO3, with a value D*= 0.08 (cm3/J)1/2, appears to out perform Pb based pyroelectric thin films, thus making it a viable candidate for IR pyroelectric detector applications.

Pyroelectric properties of Pb(Zr,Ti)O3 and Pb(Zr,Ti)O3/PbTiO3 multilayered thin films

Pyroelectric infrared (IR) arrays with 2×8 elements were developed using the PbZr0.3Ti0.7O3 (PZT) thin films and multilayered PbZr0.3Ti0.7O3/PbTiO3 (PZT/PT) thin films. At 1 kHz, dielectric constant of 389 and 558, dielectric loss of 0.012 and 0.011 were obtained for the PZT/PT and PZT thin films. The pyroelectric coefficients for the PZT/PT film and the PZT film were 380 and 400 μC/m2K. The detectivity figures of merit for the PZT/PT and PZT thin films were 20.3×10−6 Pa−1/2, and 18.7×10−6Pa−1/2, and the voltage response figures of merit were 0.038 m2/C and 0.028 m2/C, respectively. At 60 Hz radiation modulation frequency, the specific detectivity with an element size of 240×360 μm2 was 2.6×108 Hz1/2cm/W and 1.8×108 Hzl/2cmAV respectively. These experimental results show that the sensing element made of multilayered thin films is a better choice in developing high performance IR detectors.

Micro-machined Pyroelectric Infrared Detector Based on Sol-gel Derived Pb(Zr0.3Ti0.7)O3/PbTiO3 Multilayer Thin Films

AbstractA sol-gel derived Pb(Zr0.3Ti0.7)O3/PbTiO3 (PZT/PT) multilayer thin film structure has been studied for the application of infrared detection. Compared to the pure Pb(Zr0.3Ti0.7)O3 (PZT) thin film deposited by the same process, the multilayer thin film shows a lower dielectric constant and similar pyroelectric coefficient and dielectric loss. The detectivity figures of merit for the PZT/PT and PT thin films are 20.3×10−6 Pa-1/2 and 18.7×10−6 Pa−1/2, and values of voltage response figures of merit are 0.038 m2/C and 0.028 m2/C, respectively. The results show that the multilayer PZT/PT film is a better choice for pyroelectric infrared detection. Pyroelectric infrared detectors have been successfully developed based on the multilayer PZT/PT thin film. A silicon bulk-machined thermal isolation structure has been applied to reduce thermal loss from the sensing thin film to the Si substrate. To evaluate the detector performance and to aid in the thermal structure design, finite element analysis (FEA) of the detector in terms of heat transfer has been carried out by using a software package “ANSYS”. The detector response has been characterized by a modified Chynoweth system. At 7 Hz, the dynamic pyroelectric voltage responsivity is measured to be 108 V/W (in rms) with the sensing element size of 240×360 μm2. The measured results are consistent with the simulated results.

Independent optimization of capillary electrophoresis separation and native fluorescence detection conditions for indolamine and catecholamine measurements.

Separation conditions in capillary electrophoresis with native fluorescence detection often represent a compromise in terms of the separation and detection figures of merit. As both the separation and fluorescence properties greatly depend on pH, the ability to independently optimize pH in the separation capillary and the detection region can improve many complex separations. When using a sheath flow cell, the pH at the detection zone can be adjusted independently of the electrophoresis buffer pH. Using capillary electrophoresis with 257-nm excitation and native fluorescence detection, more than an order of magnitude improvement in the limits of detection for dopamine (from 1400 to 120 nM) and epinephrine (from 850 to 60 nM) is achieved by maintaining the basic separation conditions and an acidified sheath buffer. The detection of dopamine in an individual Aplysia californica cerebral ganglion neuron is demonstrated.

Pyroelectric detection properties of gadolinium molybdate (gmo)

The pyroelectric detection properties of gadolinium molybdate (GMO) crystals have been studied near and at its 159°C ferroelectric transition temperature. Responsivity and detectivity figures of merit are calculated from measurements of pyroelectric currents induced by white light irradiation and are compared with room temperature figures of merit for TGS and SBN detectors. Since GMO does not exhibit a dielectric anomaly, it can be used as a threshold detector by heating through the transition temperature from a pre-selected temperature increment below the transition. Voltage-sensitive pyroelectric currents at the transition, found previously, permit voltage control of the threshold.