Fine-patterning of sol-gel derived PZT film by a novel lift-off process using solution-processed metal oxide as a sacrificial layer

Sub-5 µm pattern of sol-gel derived lead-zirconium-titanate (PZT) film with a thickness of 80–390 nm was successfully prepared on Pt(111)/TiO_x/SiO₂/Si (100) substrate by a novel lift-off process using solution-processed metal oxides as a sacrificial layer. The process is simply divided into three steps: In-Zn-O (IZO) sacrificial layer spin-coating and patterning, PZT film formation followed by lift-off process. The results suggested that the IZO layer is effective in preventing PZT crystallization because of its thermal stability during PZT post-annealing, and its barrier-effects between the spin-coated PZT precursor and the Pt/TiO_x substrate. Consequently, the micro-pattern of lift-off PZT exhibited better properties than that formed by wet-etching. In particular, the lift-off PZT films possessed better ferroelectric properties, higher break-down voltage, and more well-defined shape than those of films patterned by conventional wet-etching. This lift-off process shows great promise for highly integrated devices due to its fine pattern-ability.     

Microwave enhanced sintering of tape-cast ferroelectric films

Porous Pb(Zr_xTi_1−x)O₃(PZT) thick films that had been prepared by tape casting were densified by microwave energy. The microwave absorption effect is substantially correlated with the film thickness. In microwave-processed PZT thick films, rapid particle necking causes densification with no grain growth nearly in a short treatment time of 20 min at 820 °C. The same porous PZT thick films are difficult to densify in a conventional process. A 30-μm-thick PZT thick film has a pure perovskite structure. Self-supporting PZT thick films with a crack-free and uniform microstructure formed in a microwave process have larger coercive field than conventionally processed bulk PZT. The polarization, 14 μC/cm², of PZT thick films in a microwave process exceeds that, 7 μC/cm², of PZT bulk formed in a conventional process.     

Preparation of ultrathin PZT films by a chemical solution deposition method from a polymeric citrate precursor

Ultrathin PZT film was prepared using a chemical solution deposition method from polymeric citrate precursors. The PZT solution was spin-coated on an amorphous silica layer formed on a Si(1 0 0) substrate. The films were thermally treated from the substrate side with a low heating rate (1°/min) up to 700 °C and finally annealed for 10 h. Ultrathin PZT films without microstructural instability were prepared in spite of high temperature and long annealing time. AFM and HRTEM investigations revealed the formation of a well-developed dense microstructure consisting of spherical crystallites (4–7 nm). Low roughness (2.2 nm) of a ～26 nm thick layer was obtained for a two-layered PZT film. The grazing incidence X-ray diffraction (GIXRD) measurements confirmed the polycrystalline structure of ultrathin PZT films. Also, GIXRD and electron energy dispersive X-ray (EDS) analysis showed that compositional variations were smaller than expected, in spite of the long annealing time.     

Effect of O2 plasma pretreatment on structural and optical properties of ZnO films on PES substrate by atomic layer deposition

ZnO films were deposited on the O₂ plasma treated polyethersulfone (PES) substrates by atomic layer deposition. X-ray diffraction (XRD) measurements reveals that the grains in ZnO films show strongly (0 0 2) preferential orientation, when the duration of plasma pretreatment increases. The decreased grain size and improved crystallinity results in the decreased surface roughness of ZnO films. In contrast, when the duration of plasma pretreatment increases to 60 min, the surface roughness increases again due to the increased grain size and worse crystallinity. In photoluminescence measurement, slight blue shift of near-band-edge emission occurs with increasing duration of plasma pretreatment up to 30 min.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.     

Laser-transfer processing of functional ceramic films

Pulsed excimer laser irradiation through a UV-transparent fabrication substrate has been successfully employed to separate PZT thick films from their sapphire host substrates. Films of 20 μm in thickness were prepared by a hybrid particle sol–gel synthesis route. The microstructure, morphology and ferroelectric properties of the thick films after laser-transfer have been examined. Films were irradiated with a 248 nm, 15 ns pulse, and transferred to a platinised silicon substrate (Pt/Ti/SiO₂/Si). A laser fluence of 250 mJ/cm² was sufficient to delaminate the original PZT/sapphire interface. The pulsed energy density used here is lower than reported by other groups utilising a laser-transfer process for PZT. This is believed to be due to higher levels of porosity at the film/substrate interface in this study.     

Bottom electrode crystallization of PZT thin films for ferroelectric capacitors

The bottom electrode crystallization (BEC) method was applied to the crystallization of PZT thin films deposited by laser ablation over Si/SiO₂/Ti(Zr)/Pt structures, with the platinum films being deposited at two different temperatures. The results were compared with those obtained by rapid annealing with halogen lamps and furnace annealing. PZT films crystallized over Pt made at lower temperature with Ti adhesion layers tend to have a (1 1 1) preferential orientation, while those deposited on platinum made at higher temperature tend to have a (1 0 0)/(1 1 1) mixed orientation. When Zr adhesion layers are used, the PZT films crystallized over Pt have a preferential (1 0 0) orientation, except for films deposited over Pt made at 500 °C and crystallized with a high heating rate. The ferroelectric properties of the films crystallized with the BEC method are good, being similar to those obtained with the other crystallization methods using the same parameters.     

Electrohydrodynamic atomization deposition and mechanical polishing of PZT thick films

In this work, electrohydrodynamic atomization deposition, combined with mechanical polishing, was used for the fabrication of dense and even PZT thick films. The PZT slurry was ball-milled and the effect of milling time on the characteristics of the deposited films was examined. A time of 50 h was found to be the optimum milling time to produce dense films. It was found that the PZT thick films presented rough surface after deposition. In order to overcome this drawback the mechanical polishing process was employed on the deposited films. After the mechanical polishing the roughness (Ra) and peak-to-peak height (Rz) of the film surface were decreased from 422 nm to 23 nm and from 5 µm to 150 nm, respectively. Subsequently, an increase of ~10 pC N⁻¹ on piezoelectric constant (d_{33, f}) was obtained. In addition, it was observed that the d₃₃ was increased from 57 pC N⁻¹ to 89 pC N⁻¹ when the thickness was increased from 10 µm to 80 µm.     

Structural and electrical properties of Pb(Zr0.53Ti0.47)O3 films prepared on La0.5Sr0.5CoO3 coated Si substrates

PbZr_0.53Ti_0.47O₃ (PZT) thin films with thickness of 0.9 μm were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates. Both PZT and LSCO were prepared by the sol–gel method. The concentration of LSCO sol was varied from 0.3 to 0.1 mol/L, which could modify the preferential orientation of PZT thin films and consequently affect the dielectric and ferroelectric properties. The LSCO electrode layers derived from lower sol concentration of 0.1 mol/L have much more densified structure, which facilitates the formation of (1 0 0) textured PZT films with smooth and compact columnar grains. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Enhanced ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3–0.05PbTiO3 thin films with Pb(Zr0.52,Ti0.48)O3 seed layer

0.95Pb(Sc_0.5Ta_0.5)O₃–0.05%PbTiO₃ (PSTT5) thin films with and without a Pb(Zr_0.52,Ti_0.48)O₃ (PZT52/48) seed layer were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering. X-ray diffraction patterns indicate that the PSTT5 film with a PZT52/48 seed layer exhibited nearly pure perovskite crystalline phase with highly (4 0 0)-preferred orientation. Piezoresponse force microscopy observations reveal that a large out-of-plane spontaneous polarization exists in the highly (4 0 0)-oriented PSTT5 thin film. The PSTT5/PZT(52/48) possesses good ferroelectric properties with large remnant polarization P_r (12 μC/cm²) and low coercive field E_c (110 kV/cm). Moreover, The perfect butterfly-shaped capacitance–voltage characteristic curve and the relative dielectric constant as high as 733 is obtained in this PSTT5 thin film at 100 kHz.     

Increase of Mn solubility with decreasing grain size in ZnO

Nanograined (grain size 20 nm) ZnO films with various Mn content (from 0 to 47 at%) were synthesized by the novel wet chemistry method. The solubility limit for Mn was determined at 550 °C. The lattice parameter c of the ZnO-based solid solution with wurzite structure ceases to grow at 30 at% Mn. The peaks of the second phase (Mn₃O₄ with cubic lattice) become visible in the X-rays diffraction spectra at 30 at% Mn. The same second phase appears in the bulk ZnO already at 12 at% Mn. The recently published papers on the structure and magnetic behaviour of Mn-doped ZnO allowed us to obtain the size-dependence of Mn solubility in ZnO for the polycrystals and small single-crystalline particles. The overall Mn solubility drastically increases with decreasing grain size. The quantitative estimation leads to the conclusion that, close to the bulk solubility limit, the thickness of an Mn-enriched layer is several monolayers in GBs and at least two monolayers in the free surfaces.     

Impact of Sr-doping on structural and electrical properties of Pb(Zr0.52Ti0.48)O3 thin films on RuO2 electrodes

In this paper, we investigated the impact of Sr-doping on the structural properties and electrical characteristics of lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films deposited on RuO₂ electrodes by a sol-gel process and spin-coating technique. We used X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy to explore the structural, morphological, chemical, and microstructural features, respectively, of these films as a function of the growth condition (strontium doping concentrations varied from 1, 3, and 5 mol%). The PZT thin film processed at the 3 mol% Sr exhibited the best electrical characteristics, including a low leakage current of 2.27×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a large capacitance value of 2.74 μF/cm² at a frequency of 10 kHz, and a high remanent polarization of 37.95 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of strontium in the PZT film forming a perovskite structure and a thicker interfacial layer at the PSZT film-RuO₂ electrode interface.     

Tuning electrical properties of PZT film deposited by Pulsed Laser Deposition

The variation of the chemical composition and properties of PZT films as a function of oxygen pressure and laser fluence during pulsed laser deposition is used to tune the electrical properties of the PZT thin films. It is found that the deposition using a 248 nm laser fluence of 1.7 J/cm² and an oxygen pressure of 400 mtorr results the PZT films very similar to that of target material. Changing the laser fluences or oxygen pressure, affects the lead content of the deposited film. In the range of oxygen pressure 50–200 mtorr, the Zr/Zr+Ti and Ti/Zr+Ti ratio varies with oxygen pressure while the Pb/Zr+Ti ratio is almost uniform. Using oxygen pressure as a control parameter to tune the chemical compound and electrical properties of the deposited PZT films, the remnant polarization of the PZT films is tuned in the range of 6.6–42.2 µC/cm², the dielectric constant is controlled in the range of 29–130, and the piezoelectric constant d₃₃ is controlled in the range of 3.82–4.96 pm/V for a 40 nm thick PZT film.     

Improved hydrophilicity of zinc oxide-incorporated layer-by-layer polyelectrolyte film fabricated by dip coating method

ZnO nanoparticles suspended in poly(acrylic acid) (PAA) were deposited onto layer-by-layer (LBL) polyelectrolyte (PET) films fabricated from poly(allylamine hydrochloride) (PAH) and PAA by dip coating method. Effect of etching time and concentration of ZnO suspension on hydrophilicity of the LBL-PET films before and after UV irradiation was examined using water contact angle measurement. 2.0 M PAH/PAA solutions with a dipping speed of 3.0 cm/min provided stable LBL-PET films with thickness sufficient for HCl etching. Glass substrates with the etched LBL-PET film dipped into 0.2 wt.% ZnO suspension exhibited the contact angle of 10° after irradiated by UV for 60 min.     

Layered composite thick films for dielectric applications

Electrophoretic deposition has been successfully used for the preparation of multilayer composite thick films of the temperature stable microwave dielectric ceramics BaLa₄Ti₄O₁₅ (BLT) (?_r = 44, Qf₀ = 44,000 GHz) and Ba₄Nd_9.33Ti₁₈O₅₄ (BNT) (?_r = 82, Qf₀ = 10,000 GHz). The composites exhibit permittivity intermediate between the end members that may be tuned by modifying the ratio between and/or thickness of each layer, thereby tailoring the films for specific applications. In demonstrating an alternative way to tailor functional properties, these results have broad implications for a large number of thick film-based devices.     

Patterned Zn-seeds and selective growth of ZnO nanowire arrays on transparent conductive substrate and their field emission characteristics

A method for the patterned growth of ZnO nanorods with better field emission properties is presented that combines nanoimprinting, electroplated Zn seeds and aqueous solution growth of ZnO. A patterned Zn layer over large area was prepared using the poly(dimethylsiloxane) (PDMS) template to pattern PMMA masking layer without residual layer. ZnO nanorods were selectively deposited on the Zn seeds instead of growing on the bare ITO regions due to the preferred growth on Zn seeds/ITO substrate. The diameter of ZnO nanorods was decided by the concentration of reactants of zinc nitrate and hexamethyltetramine (C₆H₁₂N₄) (0.025–0.1 M) at low temperature. This approach provides the capability of creating patterned 1D ZnO micro/nanopatterns at low temperature, ambient condition, and low cost with large area on flexible devices.     

Micromoulding of PZT film structures using electrohydrodynamic atomization mould filling

In this work, electrohydrodynamic atomization combined with a photolithography polymeric micromoulding technique was used to form PZT ceramic structures. PZT thick film structures consisting of squares and rectangles of various sizes and separations were produced and used to evaluate the process. An expansion effect of approximately 10 μm on the ceramic structure width relative to the 200 μm wide mould design was observed. The minimum continuous gap between features achieved using this process was 13.5 μm, and the smallest regular PZT square structure obtainable was 106 μm in width. A sloping side wall of the PZT structures caused by the shielding of the photoresist mould was also observed in the process. The resulting PZT structures had a homogenous microstructure and exhibited a relative permittivity of 250, d_33, f of 67 pCN^?1 and remnant polarisation of 8.8 μC/cm².     

Fast removal of surface damage layer from single crystal diamond by using chemical etching in molten KCl + KOH solution

To fast remove the surface damage layer from single-crystal-diamond, we have developed a chemical etching process using molten KCl and KOH solution at high temperature around 1100 °C. High removal rate about R_{001} = 2.0 μm/h, R_{101} = 20 μm/h and R_{111} = 26 μm/h was achieved for the {001} sample surfaces, {101} and {111} sample edges, respectively. Laser microscope observation has confirmed that the {001} surface flatness has been greatly improved after etching and surface roughness formed during previous lift-off process has been effectively removed.     

Electrophoretic deposition of Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thick film on Pt wire

0.2PbNi_1/3Nb_2/3–0.8Pb(Zr,Ti)O₃ (PNN–PZT) thick films were deposited on Pt wire with the diameter of 50 μm by electrophoretic deposition (EPD) method. The EPD deposition times on the microstructures of PNN–PZT thick films were investigated. By optimizing the EPD process, the Pt wire can be uniformly wrapped with the PNN–PZT powders. During the sintering process, the as-deposited PNN–PZT/Pt wires were buried in the mixed powders of PbCO₃ and ZrO₂, and then sintered in the optimal temperature to get a dense microstructure. The piezoelectric properties of the thick films were characterized by scanning force microscopy (SFM) method. The results show that the PNN–PZT thick films prepared by EPD method have good piezoelectricity.     

Dielectric and optical properties of electroceramic PBZNZT thin films prepared by pulsed laser deposition process

The 0.6[0.94Pb(Zn_1/3Nb_2/3)O₃ + 0.06BaTiO₃] + 0.4[0.48(PbZrO₃) + 0.52(PbTiO₃)], PBZNZT, thin films were synthesized by pulsed laser deposition (PLD) process. The PBZNZT films possess higher insulating characteristics than the PZT (or PLZT) series materials due to the suppressed formation of defects, therefore, thin-film forms of these materials are expected to exhibit superior ferroelectric properties as compared with the PZT (or PLZT)-series thin films. Moreover, the Ba(Mg_1/3Ta_2/3)O₃ thin film of perovskite structure was used as buffer layer to reduce the substrate temperature necessary for growing the perovskite phase PBZNZT thin films. The PBZNZT thin films of good ferroelectric and dielectric properties (remanent polarization P_r = 26.0 μC/cm², coercive field E_c = 399 kV/cm, dielectric constant K = 737) were achieved by PLD at 400 °C. Such a low substrate temperature technique makes this process compatible with silicon device process. Moreover, thus obtained PBZNZT thin films also possess good optical properties (about 75% transmittance at 800 nm). These results imply that PBZNZT thin films have potential in photonic device applications.