Bismuth zinc niobate pyrochlore dielectric thin films for capacitive applications

Abstract

Bi 2 O 3 –ZnO–Nb 2 O 5 pyrochlore thin films were prepared on platinum coated Si wafers using a metalorganic deposition process. The structures, morphologies, and dielectric properties of films with two compositions: (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 and Bi2(Zn1/3Nb2/3)2O7, were investigated. Thin films of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 have a cubic pyrochlore phase when crystallized at 550 °C or higher. The crystal structure of Bi2(Zn1/3Nb2/3)2O7 thin films was dependent on the firing temperature; the films showed the cubic pyrochlore phase at temperatures below 650 °C, and a pseudo-orthorhombic pyrochlore structure at 750 °C. A mixture of cubic and pseudo-orthorhombic structures was found in thin films crystallized at 700 °C. (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films fired at 750 °C had a dielectric constant of ∼150 and a negative temperature coefficient of capacitance of −400 ppm/°C. Bi2(Zn1/3Nb2/3)2O7 thin films fired at 750 °C had a smaller dielectric constant of ∼80 and a positive temperature coefficient of capacitance of 150 ppm/°C. The dielectric constants of the thin films are composition, structure, and firing temperature dependent. The loss tangents of both types of films were smaller than 0.008. Bias voltage dependence of dielectric constant showed that the cubic (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films fired at 750 °C were tunable, while the pseudoorthorhombic Bi2(Zn1/3Nb2/3)2O7 films were nearly field independent. The relatively large dielectric constants, small loss tangents, controllable temperature coefficients of capacitance, and tunability of the dielectric constant suggests that Bi2O3–ZnO–Nb2O5 thin films have potential applications for integrated microwave components and decoupling capacitors.

Synthesis, structure and electrical properties of Mg-, Ni-codoped bismuth niobates

“…It is not typical for the pyrochlore structure. The best agreement between theoretical and observed X-ray patterns was obtained for the model designated as 3 and is in agreement with the pycnometric density value. Thus assumed amount of about 15-20% vacant sites in Bi sublattice seems to be in agreement with the experimental results obtained in the present study.…”

“…In most cases, doping leads to the permittivity decrease and to the tangent loss increase. However, electrical properties of several systems were investigated in the high temperature range (up to 700 °C) only in order to determine their conductivity mechanism [3,9,[19][20]27]. In our previous work [28][29] we have determined that the dielectric constant of the Bi 1.6 Cu x Mg 0.8-x Nb 1.6 O 7-δ pyrochlores behave unusually passing through a maximum (250-350 °C) with temperature increasing.…”

“…The most attention has been paid to the Zn-, Mg-containing bismuth niobates, which possess high dielectric constant (170-180) and low dielectric loss (~10 -4 ) at 1 MHz (at room temperature) [1][2][3][4][5][6][7][8][9]. To search for the same properties Fe- [10], Mn- [11][12], Co- [13], Ni- [12,[14][15], Cu- [12] and the mixed Zn-M (M -Sr [16], Ca [16][17], Mn [16,18], Ti [19][20][21][22], Sn [19,22], Zr [19,[21][22], Ce [19,22], Gd [21], Ta [23], La [24]), Mg-M (M -Sr [25], Nd [26], Cu [27]) bismuth niobates and other ones were synthesized.…”

Displacive disorder in three high-k bismuth oxide pyrochlores

“…A good example of this is the system (Bi 1.5 Zn 0.5 )(Nb 1.5 Zn 0.5 )O 6 O 0 which displays a high dielectric constant as well a some field tunability, but remains paraelectric down to the lowest temperature [5][6][7]. Interestingly, the attractive properties of this materials are retained in thin films [8][9][10][11].…”

Microwave dielectric properties of tunable capacitors employing bismuth zinc niobate thin films

“…For room temperature applications, thin films of ferroelectrics such as (Ba,Sr)TiO 3 (BST) have been extensively studied [1]. Recently, thin films of a nonferroelectric material, Bi 1.5 Zn 1.0 Nb 1.5 O 7 (BZN), which has the cubic pyrochlore structure [2] and a medium permittivity (170 -200), have attracted interest for tunable applications due to their very low losses (~ 5¥10 -4 [3]) and large tunabilities (55 %) [3][4][5][6] at low frequencies (~ 1 MHz). The tunability is defined as e max -e min ( ) e max , where † e min is the minimum measured permittivity at the maximum applied field, and † e max is the dielectric constant at zero bias.…”