Characteristics of thin-film NTC infrared sensors fabricated by micromaching technology were studied as a function of the thickness of membrane. The overall-structure of thermal sensor has a form of Au/Ti/NTC/SiOx/(100)Si. NTC film of Mn1.5CoNi0.5O3 with 0.5 micrometers in thickness was deposited on SiOx layer (1.2 mm) by PLD (pulsed laser deposition) and annealed at 600-800 degree(s)C in air for 1h. Au (400nm)/Ti (100nm) electrode was coated on NTC film by dc sputtering. By the results of microstructural, X-ray and NTC analysis, post-annealed NTC films at 700 degree(s)C for 1h showed the best characteristics as NTC thermal sensing film. In order to reduce the thermal mass and thermal time constant of sensor, the sensing element was built-up on a thin membrane with the thickness of 20-65mm. Sensors with thin sensing membrane show the good detecting characteristics.
An analysis of spike-like noise for the thermal detector prepared with Pb(Zr,Ti)O3-Pb(Sb0.5Nb0.5) (PZT- PSN) pyroelectric ceramics as sensing element was conducted by measuring its oven noise as a function of the JFET characteristics, gate resistance, low-temperature heat treatment, chemical composition and grain size of pyroelectric ceramic. Pyroelectric wafers were prepared by mixed oxide technique, and thermal sensor fabricated with a PZT-PSN ceramic wafer, JFET, chip-type gate resistor and TO- 5 package with AR coated Si-window. White noises depended on the characteristics of JFET, gate resistance and chemical composition of puyroelectric materials. Output spikes originated in JFET were removed by the pyroelectric sensing wafer with high capacitance. Pyroelectric element generated the temperature-induced transient noise during cooling, which were remarkably reduced in their amplitude and frequency by heat-treating at low temperature and by decreasing the grain size of pyroelectric ceramic. The spike-like transient noise is caused by the twinning and domain switching to reduce the thermally induced elastic energy within the sensing element, originated in the different thermal expansion between pyroelectric ceramic and alumina substrate.
The pyroelectric thermal detectors were prepared with lead zirconate titanate (PZT) ceramics, where a signal electrode had a structure of Au/metallic buffer/(PZT ceramic). The effect of buffer layer on the voltage responsivity was investigated with a response to step signal, taken by dynamic pyroelectric measurement. Pyroelectric ceramic wafer was prepared by mixed oxide technique. Au layer (thickness: 50 nm) and metallic buffers (thickness: 0 - 20 nm) of Cr, NiCr (80/20), and Ti were prepared by dc magnetron sputtering. In order to improve the light absorptivity, an Au-black was coated on Au signal electrode by thermal evaporation. At steady state, the output voltage (Vo) was decreased with increasing chopping frequency in the range of 1 - 100 Hz. A sensor without buffer showed the severe time-drift and instability in the output signal. However, the sensors with buffer layer showed the stable outputs. For step radiations, rising time (tp), peak voltage (Vp), and initial slope (k) of the output voltage were dependent upon the thickness and materials of buffer layer. The mechanical and electrical contacts between Au electrode and PZT ceramics were improved by inserting the metallic buffer layer. Considering the characteristics of the output voltage, the optimum thickness of buffer layer was about 15 - 20 nm, and the sensors with Ti buffer of 15 - 20 nm in thickness showed the good detectivity. Therefore, the stability and reliability of the thermal sensors could be improved by use of appropriate buffer layer.
Bilevel quantization using dither is useful with coarse quantizers. So we study it from a statistical viewpoint, furthermore, physical energy theory known as Hopfield neural network or Ising spin system. These are equivalent internally and they should be related to the optimum convergence or minimum quantization error of dithering. In this paper, we show this relationship and theoretical improvements.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.