BZN Thin Films Research Articles

Effect of ZnO buffer layer on the structural and electrical properties of Bi1.5Zn1Nb1.5O7 thin films grown by pulsed laser ablation

The effect of ZnO buffer layer on the growth and dielectric properties of Bi1.5Zn1Nb1.5O7 (BZN) thin films deposited on Pt-Si substrate using pulsed laser ablation was studied in detail. An intermediate ZnO buffer greatly enhanced the crystalline quality as well as the dielectric properties of BZN thin films. Variation of Raman spectra with oxygen partial pressure was studied in detail. The presence of the ZnO buffer layer has increased the dielectric constant as well as tunability. This enhancement in dielectric properties may be attributed to the increased crystallinity and oxygenation of the BZN thin films in the presence of a semiconducting buffer layer. The directly stacked structure of the fabricated device with the top dielectric oxide thin films as a gate oxide and the semiconducting buffer layer as the channel layer can be used as a potential candidate for thin film field effect transistor applications.

Pyrochlore structure and dielectric properties of bismuth zinc niobate thin films prepared by RF sputtering

Abstract Bi 1.5 Zn 1.0 Nb 1.5 O 7 (BZN) thin films with thickness from 60 nm to 200 nm were prepared by radio-frequency magnetron sputtering and post-annealed from 550 °C to 650 °C. The x-ray diffraction results indicated that the BZN thin films possessed a cubic pyrochlore phase. The BZN thin films exhibited thickness-independent dielectric properties with dielectric constant of ~180 and low loss tangent less than 1% at 10 kHz as the film thickness decreased to 60 nm. The BZN thin films with thickness of 200 nm and post-annealed at 650 °C had a tunability of 32.7% at a DC bias field of 1.5 MV/cm. The results suggest that the BZN thin films have promising applications on the embedded capacitors, tunable devices and energy storage devices.

RETRACTED: Effect of thickness of Bi1.5Zn1.0Nb1.5O7 gate insulator on performance of ZnO based thin film transistors

s The bottom-gate structure ZnO based thin film transistors (ZnO-TFTs) using Bi1.5Zn1.0Nb1.5O7 (BZN) thin films as gate insulator were fabricated on Pt/SiO2/Si substrate by radio frequency magnetic sputtering at room temperature. We investigated the effect of thicknesses (100 nm, 170 nm, 250 nm, and 330 nm) of BZN thin films on the performance of BZN thin films and ZnO-TFTs. The results show that 170-nm-thick BZN thin film obtained high dielectric constant of 71, low roughness of 3.51 nm and low leakage current density of 10−7 A/cm2, which is approximately one order magnitude lower than that of 100-nm-thick BZN thin film. Also, we concluded that the electrical performance of ZnO-TFTs using 170-nm-thick BZN thin film as gate insulator is enhanced remarkably. On/off current ratio (1.1 × 105) and field effect mobility (0.22 cm2/Vs) of ZnO-TFTs are approximately one order magnitude and seven times larger, respectively than that of ZnO-TFTs using 100 nm-thick BZN thin film as gate insulator. Meanwhile, surface states density (3.21 × 1012) of ZnO-TFTs is reduced three times.

Effect of annealing temperature of Bi1.5Zn1.0Nb1.5O7 gate insulator on performance of ZnO based thin film transistors**Project supported by the National Natural Science Foundation of China (Nos. 51332003, 51202184), the International Science & Technology Cooperation Program of China (Nos. 2010DFB13640, 2011DFA51880), and the “111 Project” of China (No. B14040).

The bottom-gate structure ZnO based thin film transistors (ZnO-TFTs) using Bi1.5Zn1.0Nb1.5O7 (BZN) thin films as gate insulator were fabricated on Pt/SiO2/Si substrate by radio frequency magnetic sputtering. We investigated the effect of annealing temperature at 300, 400, and 500 °C on the performance of BZN thin films and ZnO-TFTs. XRD measurement confirmed that BZN thin films were amorphous in nature. BZN thin films annealed at 400 °C obtain the high capacitance density of 249 nF/cm2, high dielectric constant of 71, and low leakage current density of 10−7 A/cm2 on/off current ratio and field effect mobility of ZnO-TFTs annealed at 400 °C are approximately one order of magnitude and two times, respectively higher than that of ZnO-TFTs annealed at 300 °C. When the annealing temperature is 400 °C, the electrical performance of ZnO-TFTs is enhanced remarkably. Devices obtain a low sub-threshold swing of 470 mV/dec and surface states density of 3.21 × 1012cm−2.

Study on the electrical properties of ZnO thin film transistors using pyrochlore Bi1.5Zn(1+y)Nb1.5O(7+y)gate insulators fabricated by RF sputtering

Abstract. A series of ZnO thin film transistors (TFTs) using pyrochlore Bi 1.5 Zn ð1þyÞ Nb 1.5 O ð7þyÞ (BZN) thin filmsas gate insulators by RF sputtering has been fabricated. The relations between the zinc content and perfor-mance of BZN thin films and ZnO-TFTs are studied. The electrical properties of the ZnO-TFTs with BZNgate insulators as a function of Zn content are discussed. The research results showed that excess Zn(5 mol.%) can significantly enhance the performance of BZN thin films and ZnO-TFTs, which is mainly attributedto the compensation of Zn volatility during fabrication of BZN thin films. At an applied electric field of 250 kV∕cm,the leakage current density of BZN thin films with 5 mol.% excess Zn is approximately four order of magnitudelower than that of BZN thin films without excess Zn. The subthreshold and surface state density of ZnO-TFTswere decreased from 684 and 350 mV∕dec to 4.5×10 12 and 2×10 12 cm −2 , respectively, as Zn content wasincreased. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.55.6.067106]

Bismuth Zinc Niobate Thin Film Multilayer Capacitors with Cu Electrodes Fabricated at Low Temperature by RF Magnetron Sputtering

Thin film multilayer capacitors (MLCs) composed of amorphous Bi1.5Zn1.0Nb1.5O7 (BZN) dielectric layers with Cu internal electrodes were fabricated by radio‐frequency magnetron sputtering at a temperature below 150°C. Both BZN thin films and Cu internal electrodes were deposited in situ through a set of steel shadow masks at room temperature and postannealed at 150°C. The BZN dielectric layers used in the MLCs are amorphous and the thickness for each BZN layer is approximately 220 nm. Metallic Cu layer used as the internal electrode is about 50 nm thick. Auger electron spectroscopy analysis indicates that there are no diffusion between BZN films and Cu electrodes, as well as no oxidation of Cu electrodes during the fabrication process owing to room‐temperature deposition and low‐temperature postannealing (150°C). The thin film MLCs with different number of BZN layers were fabricated. The thin film MLCs with five BZN layers exhibit promising properties with dielectric constant of 72, capacitance density of 1600 nF/cm2, and loss tangent of 5.4% at 10 kHz. These results suggest that the BZN thin film MLCs have potential applications for the embedded PCBs.

Effect of sputtering power on properties of ZnO thin film transistors with Bi1.5Zn1.0Nb1.5O7 gate insulator

ZnO based thin film transistors (ZnO-TFTs) exhibit high field effect mobility, high drive capability, low operating voltage, low sub-threshold swing and low gate-leakage current. In this work, ZnO-TFTs with Bi1.5Zn1.0Nb1.5O7 (BZN) gate insulator were fabricated by radio frequency magnetron sputtering at low temperature (500°C). Pyrochlore BZN thin films were deposited onto Pt/TiO2/SiO2/Si substrates under different sputtering powers from 110W to 190W. The influence of sputtering power on dielectric properties of BZN thin film has been investigated. The capacitance density and dielectric constant increase from 165nF/cm2 to 230nF/cm2 and from 48 to 66, respectively, while the loss tangent reduces from 1.7% to 0.8% with increasing sputtering power. BZN thin films are amorphous in nature and have dense and smooth surface. The roughness of BZN thin films decreases from 6.70nm to 3.67nm with increasing sputtering power. The influence of sputtering power on electrical properties of ZnO-TFTs with BZN gate insulator has also been studied. The field effect mobility, current on/off ratio and saturation current increase from 0.026cm2/Vs to 0.18cm2/Vs, from 103 to 105 and from 0.1µA to 2.79µA, respectively. While the sub-threshold swing decreases from 689mV/dec. to 384mV/dec., threshold voltage is less than 4V. ZnO-TFTs with BZN gate insulator exhibit the optimized electrical properties at sputtering power of 150W, which also result in the formation of a smooth surface at the oxide/channel interface.

Structural and dielectric properties of calcium doped bismuth zinc niobate thin films prepared by pulsed laser deposition at room temperature

(Bi1.5Zn0.1Ca0.4)(Zn0.5Nb1.5)O7 (BZNCa) thin films were prepared by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates at room temperature. The as-deposited films and films post-annealed from 100°C to 175°C for 10min in air are all amorphous. The influence of the post-annealing process on structural and electrical properties was investigated. The surface morphology of BZNCa films remains almost same with the annealing temperature. While the dielectric and leakage-current properties of the films are strongly influenced by the annealing temperature. The film deposited at O2 pressure of 4Pa and then post-annealed at 150°C shows the improved dielectric and leakage-current characteristics. The dielectric constant and loss tangent are 67.2 and 0.03at 100kHz, respectively. The leakage current density is less than 1µA/cm2 at an applied bias electric field of 400kV/cm. The results indicate that calcium doped BZN thin films have potential applications for embedded capacitors.

Domain matched epitaxial growth of Bi1.5Zn1Nb1.5O7 thin films by pulsed laser deposition

Abstract Bi 1.5 Zn 1 Nb 1.5 O 7 (BZN) epitaxial thin films were grown by pulsed laser deposition on Al 2 O 3 with a double ZnO buffer layer through domain matching epitaxy (DME) mechanism. The pole figure analysis and reciprocal space mapping revealed the single crystalline nature of the thin film. The pole figure analysis also shows a 60° twinning for the (2 2 2) oriented crystals. Sharp intense spots in the SAED pattern also indicate the high crystalline nature of BZN thin film. The Fourier filtered HRTEM images of the BZN–ZnO interface confirms the domain matched epitaxy of BZN with ZnO buffer. An electric field dependent dielectric tunability of 68% was obtained for the BZN thin films with inter digital capacitors patterned over the film.

Strain-Stable Nonlinear Dielectric Responses in Pyrochlore Bismuth Zinc Niobate Thin Films

The effect of film strain on the dielectric responses of pyrochlore Bi–Zn–Nb–O (BZN) thin films was investigated in (111)-oriented BZN thin films grown on various substrates. The bias-field dependence of dielectric constant revealed that both the linear and nonlinear electric susceptibilities of BZN thin films are stable against the film strain, unlike conventional tunable materials, such as (Ba,Sr)TiO3. The difference in dielectric nonlinearity between BZN and BST films is discussed on the basis of the phenomenological theory. The strain stability of linear and nonlinear dielectric responses of BZN is available for practical thin-film tunable applications.

A Distributed Phase Shifter Using Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3 Thin Films

We report the demonstration of a monolithic phase shifter employing Bi1.5Zn1.0Nb1.5O7 (BZN)/Ba0.5Sr0.5TiO3 (BST) thin films on sapphire substrates. The BST and BZN thin films are successively deposited by radio-frequency magnetron sputtering. A distributed phase shifter with a coplanar-waveguide transmission line periodically loaded with the BZN/BST capacitors is fabricated. The return loss of the circuit is better than −13 dB from 1 to 12 GHz, and it provides 65° phase shift with an insertion loss of −4 dB at 12 GHz. The results show that BZN/BST thin films are promising candidate dielectrics for rf/microwave tunable applications.

Bi1.5Zn1.0Nb1.5O7 thin films deposited at low temperature and post-annealed for crystallization

Near-stoichiometric Bi1.5Zn1.0Nb1.5O7 (BZN) thin films were prepared on Pt/TiO2/SiO2/Si (100) substrates at 400 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The as-deposited BZN thin films were post-annealed at 700 °C for 30 min in situ vacuum chamber (in situ) and in oxygen ambient oven (ex situ). The crystallinity, microstructure and electrical properties of BZN thin films were investigated. The X-ray diffractometer results indicate that BZN thin films deposited at 400 °C are amorphous in nature and the post-annealed thin films exhibit a cubic pyrochlore structure. The as-deposited BZN thin films show permittivity of 68 and loss tangent of 0.0011 at 10 kHz, respectively. After a post-annealing at 700 °C for 30 min, the dielectric properties of thin films are significantly improved. Permittivity and loss tangent of the in situ annealed films are 127 and 0.005 at 10 kHz, respectively. And the films post-annealed in O2 oven show the largest permittivity of 170 and tangent of 0.006. The improved dielectric properties can attribute to the crystallization of thin films. BZN thin films deposited at low temperature and crystallized at high temperature show the dielectric tunability without an electric breakdown to the maximum measurement bias voltage. And BZN thin films also show the excellent leakage current properties.

Structures and dielectric properties of pyrochlore bismuth zinc niobate thin films with zinc compensation

Pyrochlore Bi1.5Zn1.0Nb1.5O7 (BZN) thin films deposited at 650°C under an oxygen pressure of 10Pa by pulsed laser deposition were characterized as a function of zinc amount. The zinc concentration in the thin films was varied using ceramic targets having 0–40mol% excess zinc contents. The X-ray diffraction measurement shows that thin films have a cubic pyrochlore phase structure and a strong preferential orientation of (111) plane. The dielectric properties are investigated as functions of temperature and frequency. Dielectric constant and loss tangent of the thin films both slightly increase with the increase of Zn amount. The thin film with 40mol% zinc exhibits a dielectric constant of 198 and a loss tangent of 0.004 at 10kHz. The dielectric relaxation behavior has been studied by measuring the temperature dependence of dielectric properties. The characteristic temperatures (Tm) move to the high temperature with the increase of Zn and gradually approach that of BZN ceramic. Meanwhile, in a wide frequency and temperature range (1kHz–1MHz, −100–150°C), the dielectric constant of the thin films almost keeps unchanged and shows a negative temperature coefficient. Leakage current density of the thin films with 20mol% zinc is approximately three order magnitude lower than that of films with 0mol% zinc at 400kV/cm. The conduction of BZN thin films is controlled by the Schottky emission mechanism and the space-charge-limited current mechanism.

Effect of excess Bi2O3 on structures and dielectric properties of Bi1.5Zn1.0Nb1.5O7 thin films deposited at room temperature by RF magnetron sputtering

Abstract To compensate for bismuth loss that occurred during the film deposition process, Bi 1.5 Zn 1.0 Nb 1.5 O 7 (BZN) thin films were deposited at room temperature from the ceramic targets containing various excess amounts of bismuth (0–20 mol%) on Pt/TiO 2 /SiO 2 /Si substrates by using RF magnetron sputtering technique. The effect of bismuth excess content on the microstructure and electrical properties of BZN thin films was studied. The microstructure and chemical states of the thin films were studied by SEM and XPS. EPMA was employed to assess the film stoichiometry. The X-ray diffraction analysis reveals that the BZN thin films exhibit the amorphous structure in nature. An appropriate amount of excess bismuth improves the dielectric and electrical properties of BZN thin films, while too much excess bismuth leads to deterioration of the properties. BZN thin film with 5 mol% excess bismuth exhibits a dielectric constant of 61 with a loss of 0.4% at 10 kHz and leakage current of 7.26×10 −7 A/cm 2 at an electric field of 200 kV/cm.

Influences of post-annealing on structural and electrical properties of Bi1.5Zn1.0Nb1.5O7 thin films prepared by pulsed laser deposition

► BZN thin films were prepared on Pt/TiO 2 /SiO 2 /Si(100) substrates by PLD. ► After annealing, dielectric properties of thin films are significantly improved. ► Dielectric constant of the in situ annealed films is 181 at 10 kHz. ► The films post-annealed in O 2 oven show the largest dielectric constant of 202. Bi 1.5 Zn 1.0 Nb 1.5 O 7 (BZN) thin films were prepared on Pt/TiO 2 /SiO 2 /Si(100) substrates at 650 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The crystallinity, microstructure and electrical properties of BZN thin films were investigated to verify the influences of post-annealing thermal process on them. The X-ray diffractometer (XRD) results indicate that all Bi 1.5 Zn 1.0 Nb 1.5 O 7 thin films without post-annealing process or with post-annealing in situ vacuum chamber and in oxygen ambient exhibit a cubic pyrochlore structure. The improved crystallinity of BZN thin films through post-annealing was confirmed by XRD and scanning electron microscope (SEM) analysis. Dielectric constant and loss tangent of the as-deposited BZN thin films are 160 and 0.002 at 10 kHz, respectively. After annealing, dielectric properties of thin films are significantly improved. Dielectric constant and loss tangent of the in situ annealed films are 181 and 0.0005 at 10 kHz, respectively. But the films post-annealed in O 2 oven show the largest dielectric constant of 202 and the lowest loss tangent of 0.0002, which may attribute to the increase in grain size and the elimination of oxygen vacancies. Compared with the as-deposited BZN thin films, the post-annealed films also show the larger dielectric tunability and the lower leakage current density.

Structure and microwave dielectric properties of Bi1.5Zn1.0Nb1.5O7 thin films deposited on alumina substrates by pulsed laser deposition

Bi1.5Zn1.0Nb1.5O7 (BZN) thin films were deposited on polycrystalline alumina substrates by pulsed laser deposition at different substrate temperatures. The phase structure and surface morphology were characterized using X-ray diffractometer (XRD) and atomic force microscopy. Microwave dielectric properties were performed using split-post dielectric resonator method at spot frequencies of 10, 15 and 19GHz, respectively. The XRD results indicate that the as-deposited Bi1.5Zn1.0Nb1.5O7 thin films deposited at 650°C are amorphous in nature. The dielectric permittivity and loss tangent of the amorphous BZN thin films are 75.5 and 0.013 at 10GHz, respectively. As the measure frequency increased to 19GHz, the dielectric permittivity slightly decreases and loss tangent slightly increases. BZN thin films were crystallized after the post-annealing by a rapid thermal annealing in air for 30min. The crystallized BZN thin films exhibit the excellent dielectric properties and frequency responses. The dielectric permittivity and loss tangent of the crystallized BZN thin films are 154 and 0.038 at 10GHz, respectively.

The third‐order optical nonlinearity of Bi1.5Zn1.0Nb1.5O7 thin film on quartz by pulsed laser deposition

AbstractBi1.5Zn1.0Nb1.5O7 (BZN) thin films with good surface morphology were prepared on fused quartz substrates by pulsed laser deposition (PLD). The X‐ray diffraction (XRD) analysis and atomic force microscope (AFM) surface morphology measurements were performed on the samples. The XRD pattern demonstrated that the films are cubic pyrochlore structure and well crystallized. The AFM analysis indicated that the films have less rough surface. The fundamental optical constants, such as band gap, the wavelength dependence of the transmittance, and the refractive index, were obtained. The sign and magnitude of both real and imaginary parts of third‐order nonlinear susceptibility χ(3) of the BZN thin films were determined by a single beam Z‐scan technique performed at 1064 nm with a picoseconds laser. The third‐order nonlinear refractive index coefficient γ and the nonlinear absorption coefficient β of the BZN thin films are 4.06 × 10−15 m2/W and −1.45 × 10−9 m/W, respectively. The real part and the imaginary part of the third‐order nonlinear susceptibility χ(3) of the BZN thin films are 6.03 × 10−9 and 1.82 × 10−10 esu, respectively. The mechanisms of nonlinear refraction and nonlinear absorption were discussed. The results suggest that BZN thin film exhibit large third‐order nonlinear optical properties and be a promising material for applications in nonlinear optical devices.

Ferroelectric and dielectric multilayer heterostructures based on KTa0.65Nb0.35O3 and Bi1.5-xZn0.92-yNb1.5O6.92–1.5x-y grown by pulsed laser deposition and chemical solution deposition for high frequency tunable devices

Epitaxial growth of Bi1.5–xZn0.92–yNb1.5O6.92–1.5x–y (BZN) thin films was achieved on (100)pc LaAlO3 substrate by pulsed laser deposition (PLD) and by chemical solution deposition based on Pechini process. Effect of bismuth and zinc deficiency on the BZN thin films obtained by PLD was discussed, in relation with the starting target composition. Dielectric permittivity and bandgap values were determined from electrical and spectroscopic ellipsometry measurements performed on randomly oriented films grown on Pt/Si substrate. BZN thin films obtained by PLD exhibit, at 100kHz, a dielectric constant of εr=203 and quite low dielectric losses of tanδ=5×10−2. Epitaxial ferroelectric−dielectric KTa0.65Nb0.35O3 (KTN)−Bi1.5–xZn0.92–yNb1.5O6.92–1.5x–y (KTN on BZN and BZN on KTN) bilayers were obtained by PLD on (100)pc LaAlO3 with the insertion of a suitable buffer layer of KNbO3 in the case of KTN on BZN. Such multilayer heterostructures with an epitaxial growth control of each layer are promising candidates for potential integration in microwave devices.

Structures and Dielectric Properties of Bi1.5Zn1.0Nb1.5O7 Thin Films Prepared by Pulsed Laser Deposition at Low Temperature

Amorphous Bi1.5Zn1.0Nb1.5O7 (BZN) thin films have been prepared on Pt/TiO2/SiO2/Si(100) substrates by pulsed laser deposition (PLD) process at low temperature. BZN films were deposited at room temperatures under the oxygen pressure from 1 Pa to 30 Pa, and then post-annealed at the temperature below 200°C. XRD analysis indicates that BZN films are still amorphous in nature after the post-annealing. The dielectric constant of amorphous BZN films increases and the dielectric loss decreases after the post-annealing process. The dielectric properties of BZN films are strongly dependent on the oxygen pressure. BZN Thin films deposited at 1 Pa exhibit superior dielectric characteristics. Dielectric constant and loss tangent are 60.2 and 0.006 at 10 kHz, respectively. Leakage current density is less than 1 × 10−7 A/cm2 at 300 kV/cm.

Multilayer Bi 1.5Zn 1.0Nb 1.5O 7/Ba 0.6Sr 0.4TiO 3/Bi 1.5Zn 1.0Nb 1.5O 7 thin films for tunable microwave applications

Bi 1.5Zn 1.0Nb 1.5O 7/Ba 0.6Sr 0.4TiO 3/Bi 1.5Zn 1.0Nb 1.5O 7 tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5–2 nm and grain size of 100–150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO 2/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 °C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications.