Low Frequency Noises of Hydrogen Sensors

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					                     Sensors & Transducers Journal, Vol. 104, Issue 5, May 2009, pp. 58-67


                                                      Sensors & Transducers
                                                                                           ISSN 1726-5479
                                                                                            © 2009 by IFSA
                                                                               http://www.sensorsportal.com




                Low Frequency Noises of Hydrogen Sensors
     Zara MKHITARYAN, Ferdinand GASPARYAN, Armine SURMALYAN
      Department of Physics of Semiconductors & Microelectronics, Yerevan State University,
                         1 Alex Manoogian St., 0025 Yerevan, Armenia
                                     Tel.: (37410) 57 83 82
                                    E-mail: fgaspar@ysu.am


          Received: 18 February 2009 /Accepted: 19 May 2009 /Published: 25 May 2009


Abstract: The investigated sensors have sandwich structure metal/porous silicon/crystalline silicon/Al.
The contact metal on porous silicon was from Au and from Pd. Porosity of the samples is 57 % and
63 %. Current-voltage characteristics and low frequency noises spectra of crystalline silicon sensors
with nano-pores surface layer before, during and after influence of hydrogen gas flow are studied.
Sensitivity of porous silicon on H2 is determined both by the traditional resistance modulation method
and by the noise spectroscopy method. Analyses of gas sensitivity show advantages of the noise
method. Noise spectra of the samples with porous silicon layer in general have 1 f γ forms where
0.7 ≤ γ ≤ 1 . For low frequency noise modeling and for explanation of its behavior “Correlated
number-mobility fluctuation model” is used. Copyright © 2009 IFSA.

Keywords: Low frequency noise, Hydrogen sensor, Porous silicon



1. Introduction
Design and manufacture of control and monitoring systems permitted to receive important information
about composition of the several gaseous medium. This is very important for the environment
monitoring. The basic part of the control and monitoring systems is the gas sensor. At present there are
gas sensors on the base of several semiconductor materials and principles of operation. They are used
for threshold detection of the several gas escapes and for control of the foul gas concentration at the
technological processes. Extensive search for new materials and compounds, new techniques for
increasing of sensitivity, selectivity and detectivity of semiconductor based gas sensors have great
interest [1-7]. Porous silicon (PS) has high resistivity and therefore it is very sensitive to external
influences, such as gaseous medium. Porous silicon/silicon substrates have been used for sensing
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                      Sensors & Transducers Journal, Vol. 104, Issue 5, May 2009, pp. 58-67

applications. The structures are fabricated by forming a porous silicon layer on a silicon substrate and
contacting both the PS surface and the back of the substrate. Using these structures a gas sensor based
on the changing current due to the dipole moment of the gas is demonstrated in [4]. Note that PS is
successfully used for design and construction not only gas, as well as chemical, bio-sensors and air
humidity sensors [8]. Hydrogen is the most attractive and ultimate candidate for future fuel and an
energy carrier. The hydrogen gas sensors that can quickly and reliably 
				
DOCUMENT INFO
Description: The investigated sensors have sandwich structure metal/porous silicon/crystalline silicon/Al. The contact metal on porous silicon was from Au and from Pd. Porosity of the samples is 57 % and 63 %. Current-voltage characteristics and low frequency noises spectra of crystalline silicon sensors with nano-pores surface layer before, during and after influence of hydrogen gas flow are studied. Sensitivity of porous silicon on H^sub 2^ is determined both by the traditional resistance modulation method and by the noise spectroscopy method. Analyses of gas sensitivity show advantages of the noise method. Noise spectra of the samples with porous silicon layer in general have 1/ f^sup γ^ forms where 0.7 ≤ γ ≤ 1. For low frequency noise modeling and for explanation of its behavior "Correlated number-mobility fluctuation model" is used. [PUBLICATION ABSTRACT]
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