Nanocomposites and nanomaterials

Structural and electrical properties of single- and multilayered thick-film nanostructures 
H. Klym1, I. Hadzaman2, O. Shpotyuk3, I. Vasylchyshyn1

1Lviv Polytechnic National University, Bandery str., 12, Lviv-79013, Ukraine 
E-mail: halyna.i.klym@lpnu.ua; klymha@yahoo.com 
2Drohobych Ivan Franko State Pedagogical University, Ivan Franko str., 24, Drohobych-82100, Ukraine
3Vlokh Institute of Physical Optics, Dragomanova str., 23, Lviv-79005, Ukraine

Single- and multilayered thick-film nanostructures based on functional spinel  magnesium aluminates and mixed transition-metal manganite ceramics are known to be widely used for temperature and humidity measurement. In this work temperature/humidity sensitive thick films with p+-type of electrical conductivity, p-type of electrical conductivity, insulating i-type (based on MgAl2O4 ceramics), as well as p-p+, p-p+-p and p-i-p+ structures were studied.
Scanning electron microscopy micrograph of p-i-p+ thick-film structure based on p+-type Cu0.1Ni0.1Mn1.2Co1.6O4 and p-type Cu0.1Ni0.8Mn1.9Co0.2O4 ceramics reveals grains of basic ceramics, surrounded (“covered”) by glass and pores. Thick films show higher density and microstructure homogeneity with uniform distribution of grains, glass additives and pores. Contacting area of partially removed and peeled thick-film layers is evident from this micrograph. During sintering process of thick-film structures the diffusion of elements occurs from one layer into near-surface region of the next layer with other conductivity. Novel in this work is using of p+-conductive Cu0.1Ni0.1Mn1.2Co1.6O4 layers to preparation of contact area for humidity-sensitive i-type layers. Such approach eliminates diffusion processes in the contact element material to thick films. So, we prepared not only multilayer p-i-p+ structure, but increase of active adsorption-desorption surface area for humidity-sensitive thick-film layers at using of same spinel material not only as temperature-sensitive but as conductive layer.
 It is shown that increasing of the quantity of thick-film layers (from two to three) results in the improvement of the temperature sensitivity of thick-film structures. Humidity-sensitive thick films in one-layered form posses good linear dependence of electrical resistance on relative humidity without hysteresis in the range of 40-99 %. Multilayered p-i-p+ thick-film structures are stable in time and can be successfully applied for integrated environmental sensors.