Metal-ferroelectric-semiconductor Capacitor Research Articles

(Invited) Fabrication Technique of Ferroelectric HfxZr1−XO2 Thin Films Using ALD-ZrO2 Nucleation Layers

Ferroelectric HfxZr1−xO2 (HZO) thin films have attracted considerable attention towards high-density and low-power ferroelectric memory devices of ferroelectric random access memory (FeRAM) and ferroelectric field-effect transistors (FeFETs) [1]. To obtain ferroelectric orthorhombic (O) phase of HZO films, several techniques have been investigated, such as the TiN stressor layer technique [2] and controlled annealing conditions [3]. On the other hand, we pay attention to the ZrO2 nucleation layer technique because ZrO2 films deposited by atomic layer deposition (ALD) method formed a nanocrystalline structure and consisted dominantly of O, tetragonal (T), and cubic (C) phases, whose lattice constants are considerably close to that of ferroelectric O phase for HfO2 [4]. In this paper, we report the crystallinity and ferroelectricity of HZO films fabricated using the ZrO2 nucleation layer technique for metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors.First, four types of MFM capacitors of TiN/HZO/TiN (MFM w/o), TiN/HZO/bottom-ZrO2/TiN (MFM B-ZrO2), TiN/top-ZrO2/HZO/TiN (MFM T-ZrO2), and TiN/top-ZrO2/HZO/bottom-ZrO2/TiN (MFM D-ZrO2) were systematically investigated for the FeRAM applications [5]. The thicknesses of the ALD-grown HZO and ZrO2 films were 10 and 2 nm, respectively. The post-deposition annealing was performed at 600°C. The remanent polarization (2P r = P r + − P r −) of the MFM capacitors increased in the following order: MFM w/o (12 µC/cm2) < MFM B-ZrO2 (15 µC/cm2) < MFM T-ZrO2 (23 µC/cm2) < MFM D-ZrO2 (29 µC/cm2), while all capacitors showed almost the same coercive electric field (E c) value of around 1.2 MV/cm. Therefore, maximum 2P rvalue of the MFM capacitor was obtained using the top- and bottom-ZrO2 nucleation layers. For the MFM capacitors with ZrO2 nucleation layers, epitaxial-like grain growth of the HZO film occurred on the nanocrystalline top- and bottom-ZrO2 layers. Moreover, the relative ratio of O/T/C phases in the ferroelectric film, which was estimated using the peak area ratio of O(111)/T(101)/C(111)/{M(−111)+ O(111)/T(101)/C(111)+M(111)}, increased in the following order: MFM w/o < MFM B-ZrO2 < MFM T-ZrO2 < MFM D-ZrO2. Therefore, the top- and bottom-ZrO2 layers play an important role as nucleation layers for the crystallization of the HZO film, resulting in a larger relative ratio of O/T/C phases in the ferroelectric film compared to w/o. Moreover, these results indicate that the top-ZrO2 layer was more effective to form the ferroelectric phase compared to the bottom-ZrO2 layer.Next, two types of MFS capacitors of TiN/HZO/Si (MFS w/o) and TiN/top-ZrO2/HZO/Si (MFS T-ZrO2) were fabricated by low-temperature processes at 300°C of ALD and post-metallization annealing (PMA) for the FeFET applications [6]. The thicknesses of both HZO and ZrO2 films were 10 nm. Both MFS w/o and MFS T-ZrO2 were found to form an extremely thin SiO2 interfacial layer with a thickness of one or two monolayers between the HZO film and Si substrate due to a low temperature fabrication process of 300°C. The HZO film of the MFS T-ZrO2 formed O/T/C phases even with a low thermal budget of 300°C, while that of the MFS w/o had an amorphous structure. This result is attributed to the beneficial role of the nanocrystalline top-ZrO2 nucleation layer for the crystallization of an amorphous HZO film during the PMA process. Therefore, a higher 2P r value of 15 µC/cm2 was obtained for the MFS T-ZrO2 than that (2.2 µC/cm2) for the MFS w/o. Moreover, the endurance properties of the MFS T-ZrO2 were free from the wake-up effect and exhibited less degradation of switching polarization (P sw). This could be attributed to the insertion of a ZrO2 film at the TiN/HZO interface, which promoted the preferential formation of the ferroelectric orthorhombic phase and prevent the formation of oxygen vacancies at the ZrO2/HZO interface. Thus, we concluded that superior ferroelectricity with wake-up free properties and higher fatigue resistance of HZO-based MFS capacitors were achieved by using the ZrO2 nucleation layer technique.These results suggest that the fabrication technique of ferroelectric HZO films using nanocrystalline ALD-ZrO2 nucleation layers is one of the promising processes for the next-generation non-volatile memory device applications.This work was supported by JSPS KAKENHI (Nos. JP21J01667, JP20H02189, and JP18J22998) and MEXT Leading Initiative for Excellent Young Researchers (No. JPMXS0320220213).[1] T. Mikolajick et al., J. Appl. Phys. 129, 100901 (2021).[2] S. J. Kim, et al., Appl. Phys. Lett. 111, 242901 (2017).[3] S. Migita et al., Jpn. J. Appl. Phys. 58, SBBA07 (2019).[4] T. Onaya et. al., Appl. Phys. Express. 10, 081501 (2017).[5] T. Onaya et al., APL Mater. 7, 061107 (2019).[6] T. Onaya et al., APL Mater. 10, 051110 (2022).

Wake-up-free properties and high fatigue resistance of HfxZr1−xO2-based metal–ferroelectric–semiconductor using top ZrO2 nucleation layer at low thermal budget (300 °C)

Ferroelectricity and crystallinity of TiN/ZrO2/HfxZr1−xO2 (Hf:Zr = 0.43:0.57; HZO)/SiO2/Si metal–ferroelectric–semiconductor (MFS) capacitors with a top ZrO2 nucleation layer fabricated by low-temperature processes at 300 °C of atomic layer deposition and post-metallization annealing (PMA) were systematically investigated. The HZO (10 nm)-based MFS capacitors without (w/o) and with 2- and 10-nm-thick ZrO2 films (ZrO2-2 nm and ZrO2-10 nm, respectively) were found to form an extremely thin SiO2 interfacial layer (SiO2-IL) with a thickness of one or two monolayers. The HZO film in the TiN/ZrO2/HZO/SiO2/Si capacitors formed the ferroelectric orthorhombic phase even with a low thermal budget of 300 °C; in contrast, that of the w/o capacitor exhibited a predominantly amorphous structure. This result is attributed to the polycrystalline ZrO2 film acting as a nucleation layer for the crystallization of an amorphous HZO film during PMA treatment. Therefore, the remnant polarization (2Pr) increased in the order of w/o (2.2 µC/cm2) &amp;lt; ZrO2-2 nm (6.8 µC/cm2) &amp;lt; ZrO2-10 nm (15 µC/cm2). The endurance properties of the ZrO2-10 nm capacitor were free from the wake-up effect and exhibited less degradation because of the insertion of a thick ZrO2 film of 10 nm at the TiN/HZO interface, which promoted the preferential formation of the ferroelectric orthorhombic phase and prevented the formation of oxygen vacancies at the ZrO2/HZO interface. These results suggest that superior ferroelectricity with wake-up-free properties and higher fatigue resistance of HZO-based MFS capacitors can be achieved by a low-temperature fabrication technique (300 °C) using a top ZrO2 nucleation layer.

Study of SiO2 Interfacial Layer Growth during Fabrication Process of Ferroelectric HfxZr1−XO2-Based Metal-Ferroelectric Semiconductor

Recently, ferroelectric HfxZr1−xO2 (HZO) thin films have attracted much attention towards high-density and low-power ferroelectric memories such as ferroelectric field-effect transistors (FeFETs) for artificial intelligence (AI). [1] An annealing process at ≥ 300 °C is typically required to form the ferroelectric orthorhombic (O) phase of HZO films. [2, 3] It remains a big issue of an abnormal SiO2 interfacial layer (SiO2-IL) growth at the HZO/Si interface during metal-ferroelectric-semiconductor (MFS) fabrication process. It has been reported that a SiO2-IL growth led to degradation of remanent polarization (2P r) and reliability of MFS capacitors. [4] However, it is unclear how the process conditions of MFS structures, such as an atomic layer deposition (ALD) of HZO films and annealing process, affect the SiO2-IL formation in detail. In this work, we investigated a SiO2-IL growth as a function of the process temperature of ALD and annealing processes and a SiO2-IL growth of TiN/HZO/Si structures.P+-Si substrate was first cleaned using a buffered hydrofluoric acid to remove native oxide, and then an HZO film was deposited by ALD using H2O gas and (Hf/Zr)[N(C2H5)CH3]4 (Hf:Zr = 1:1) cocktail precursor. The ALD growth temperature was varied from 200 to 300 °C. A 100-nm-thick TiN film was then fabricated as gate electrode by DC sputtering. Finally, the post-metallization annealing (PMA) was carried out at 300–600 °C in an N2 atmosphere. A 3-nm-thick HZO film was used to evaluate the SiO2-IL growth using XPS analysis. On the other hand, TiN-gated MFS capacitor with a 10-nm-thick HZO film was prepared to examine electrical properties.First, the formation of the SiO2-IL was found to be negligible small at HZO (3 nm)/Si interface regardless of the ALD growth temperatures because no significant peak originating from Si-O bonds was observed in XPS spectra of Si 2p. Therefore, we employed 300 °C as an ALD temperature of HZO films for the fabrication of MFS capacitors. Next, the SiO2-IL growth as a function of PMA temperature was evaluated. The SiO2-IL growth increased as PMA temperature increased from 400 to 600 °C. Therefore, the annealing process at a lower temperature suppressed a SiO2-IL growth for the fabrication of MFS structures.Finally, polarization–electric field (P– E) measurements were conducted to evaluate the ferroelectricity of TiN/HZO (10 nm)/p+-Si MFS capacitors after the PMA process at 300–600 °C. The MFS capacitors after the PMA process at 500 and 600 °C showed breakdown during the P– E measurement due to a large leakage current. The MFS capacitor after the PMA process at 400 °C showed significantly higher 2P r value of 26 µC/cm2 compared to that (7.6 µC/cm2) after the PMA process at 300 °C. This is because the HZO films of the MFS capacitor after the PMA process at 400 °C were crystallized with the ferroelectric O phase while the HZO films had an amorphous-like structure after the PMA process at 300 °C, evaluated by X-ray diffraction (XRD). These experimental results indicated that the PMA temperature significantly affects the growth of the SiO2-IL at the HZO/Si interface while almost no difference was observed between the ALD temperature conditions.This work was partially supported by JSPS KAKENHI (JP18J22998 and JP20H02189).[1] J. Y. Kim et al., APL Mater. 9, 021102 (2021).[2] T. Onaya et al., Microelectron. Eng. 215, 111013 (2019).[3] S. J. Kim, et al., S. J. Kim et al., Appl. Phys. Lett. 111, 242901 (2017).[4] J. Mohan et al., Appl. Phys. Lett. 118, 102903 (2021).

Very large remanent polarization in ferroelectric Hf1-xZrxO2 grown on Ge substrates by plasma assisted atomic oxygen deposition

Plasma assisted atomic oxygen deposition was used to grow polycrystalline ferroelectric Hf1-xZrxO2 (x = 0.5–0.7) on technologically important (100) Germanium substrates showing sharp crystalline interfaces free of interfacial amorphous layers and strong evidence for the presence of a predominately orthorhombic phase. The electrical properties, evaluated using metal-ferroelectric-semiconductor (MFS) capacitors, show symmetric and robust ferroelectric hysteresis with weak or no wake-up effects. The MFS capacitors with x = 0.58 show very large remanent polarization up to 34.4 μC/cm2 or 30.6 μC/cm2 after correction for leakage and parasitics, combined with good endurance reaching 105 cycles at a cycling field of 2.3 MV/cm. The results show good prospects for the fabrication of Ge ferroelectric field effect transistors (FeFETs) for use in 1 T FeFET embedded nonvolatile memory cells with improved endurance.

Time-resolved simulation of the negative capacitance stage emerging at the ferroelectric/semiconductor hetero-junction

Recently, a number of papers have demonstrated sub-60 mV/decade switching by using the negative capacitance (NC) effect in ferroelectric-gate FETs. However, the physical picture is not yet understood. In this paper, an alternative physical picture for emerging NC is proposed and the development of the NC stage at the ferroelectric/semiconductor hetero-junction is described. Proposed physical picture is based on two factors, 1. “decrease in an additional voltage originated from the depolarization field by surface potential of semiconductor” and 2. “Change in the distribution ratio of gate voltage (VG) to voltage applied to the ferroelectric layer (VF) and surface potential of the semiconductor (ψS) due to the capacitance change of semiconductor.” With considering these two essential phenomena, time-resolved simulations of the NC stage emerging at the ferroelectric/semiconductor hetero-junction were carried out. This NC phenomena expressed by the negative differential of the DF for the VF, i.e. (∂DF/∂VF&amp;lt;0), emerging in the MFS (metal/ferroelectric/semiconductor) capacitor without inserting dielectric layer, are dynamically simulated to discuss the proposed NC process. The simulation results clearly reveal that the NC stage is originated from the existence of additional voltage caused by the depolarization field by surface potential of semiconductor originated from the existence of remanent polarization of ferroelectric layer, and change in the capacitance of the semiconductor during polarization switching. The different physical picture from steady-state NC and transient NC can be clearly shown.

Effects of Frequency and Bias Voltage on Dielectric Properties and Electric Modulus of Au/Bi4Ti3O12/n-Si (MFS) Capacitors

In this work, a metal-ferroelectric-semiconductor (MFS) type capacitor was fabricated and admittance measurements were held in a wide frequency range of 1 kHz-5 MHz at room temperature for the investigation of frequency and voltage dependence of complex dielectric constant, complex electric modulus and electrical conductivity of the MFS capacitor . Bismuth titanate (Bi 4 Ti 3 O 12 ) with high dielectric constant was used as interfacial ferroelectric material and the structure of MFS capacitor was obtained as Au/Bi 4 Ti 3 O 12 /n-Si. Experimental results showed that dielectric, modulus and conductivity parameters are strong functions of frequency and voltage especially in depletion and accumulation regions due to the existence of surface states (N ss ), series resistance (R s ), interfacial polarization and interfacial layer. It was found that R s of the structure and interfacial ferroelectric layer are efective in accumulation region whereas surface states (N ss ) and interfacial polarization are efective in depletion region. Also the changes in dielectric, modulus and conductivity parameters become considerably high particularly at low frequencies due to high values of R s and N ss . The observed anomalous peak in voltage dependent plots of capacitance and dielectric constant was atributed to the particular density distribution of N ss , R s and minority carrier injection. Moreover, the value of conductivity at low and intermediate frequencies is almost independent of frequency thus low frequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi 4 Ti 3 O 12 as ferroelectric interfacial layer in a MFS capacitor is preferable due to high values of its dielectric constant compared with traditional insulator layer materials such as SiO 2 and SnO 2 . Therefore, a MFS capacitor with Bi 4 Ti 3 O 12 interfacial layer can store more energy thanks to its high dielectric constant.

Tuning the resistive switching memory in a metal–ferroelectric–semiconductor capacitor by field effect structure

Resistive switching (RS) effects based on a correlation between ferroelectric polarization and conductivity might become of particular interest for nonvolatile memory applications, because they are not subjected to the scaling restrictions. Here we report on RS behaviors modulated by a reversal of ferroelectric polarization in heterostructures comprising of a ferroelectric layer and a semiconducting manganite film. It is found that electrically conducting state is bistable or even tristable; and via the polarization flipping, a maximum resistive switching coefficient (Rmax/Rmin) is found to be larger than 3000 with bias of 6V in Ag/BaTiO3/La0.8Ca0.2MnO3 at room temperature. More importantly, employing field-effect structure with ferroelectric PMN-PT as substrate, we found that the resistive switching behaviors can be tuned in situ by modulating the concentration of carriers in the semiconducting manganite layer. Possible mechanisms are discussed on the basis of the interplay of bound ferroelectric charges, charged defects in ferroelectric layer and mobile carriers in manganite thin films. The giant RS effects observed here may be of significance for memory devices by combing electronic conduction with magnetic, spintronic, and optical functionalities.

Orientation growth and electrical properties of ZnO/BaTiO3 heterostructures on silicon substrates by chemical solution deposition

Metal–ferroelectric–semiconductor (MFS) structures based on ZnO/BaTiO3 were fabricated by chemical solution deposition (CSD). The microstructure of the heterostructures was characterized by x-ray diffraction and atomic force microscopy. Both ZnO and BaTiO3 layers were found to be c-axial oriented on LaNiO3-coated silicon substrates. The morphology revealed good interface quality with root-mean-square values of about 10 nm. Compared with BaTiO3 ferroelectric thin films, the capacitance–voltage curves of Pt/ZnO/BaTiO3/LaNiO3 heterostructures exhibited a counterclockwise hysteresis loop for the MFS capacitor confirming the ferroelectric nature integrated with an n-type semiconductor. The memory windows increased and then reduced as the frequency changed from 100 kHz to 1 MHz, which can be explained by a frequency-dependent coercive field and electron injection behaviour. The current–voltage curves of ZnO/BaTiO3 heterostructure showed a good insulating characteristic. These results suggested that ZnO/BaTiO3 MFS heterostructures by CSD can be used for memory devices.

Fabrication and properties of silicon-based (Bi,Sm)4Ti3O12 thin film

Abstract Ferroelectric Bi 3.5 Sm 0.5 Ti 3 O 12 (BST) thin film has been grown on n-type Si (1 0 0) substrate by chemical solution deposition and spin coating technique. X-ray diffraction and atomic force microscope analyses confirmed that the film crystallized well at 700 °C. Metal-ferroelectric-semiconductor (MFS) configuration has been fabricated using BST as ferroelectric layer. The electrical measurements were conducted in MFS capacitor. The current–voltage characteristic displayed good insulating properties. Apparent counterclockwise hysteresis of capacitance–voltage curve for this film as the ferroelectric hysteresis was observed. The measurements of dielectric constant and dissipation factor as a function of frequency exhibited excellent dielectric properties. The MFS structure can be valuable for ferroelectric-gate field effect transistor.

Interface states of laser ablated BaTiO3 and Ba0.9Ca0.1TiO3 thin films in MFS structure determined by DLTS and C – V technique

ABSTRACTBaTiO3 and Ba0.9Ca0.1TiO3 thin films were deposited on the p – type Si substrate by pulsed excimer laser ablation technique. The Capacitance – Voltage (C-V) measurement measured at 1 MHz exhibited a clockwise rotating hysteresis loop with a wide memory window for the Metal – Ferroelectric – Semiconductor (MFS) capacitor confirming the ferroelectric nature. The low frequency C – V measurements exhibited the response of the minority carriers in the inversion region while at 1 MHz the C – V is of a high frequency type with minimum capacitance in the inversion region. The interface states of both the MFS structures were calculated from the Castagne – Vaipaille method (High – low frequency C – V curve). Deep Level Transient Spectroscopy (DLTS) was used to analyze the interface traps and capture cross section present in the MFS capacitor. There were distinct peaks present in the DLTS spectrum and these peaks were attributed to the presence of the discrete interface states present at the semiconductor – ferroelectric interface. The distribution of calculated interface states were mapped with the silicon energy band gap for both the undoped and Ca doped BaTiO3 thin films using both the C – V and DLTS method. The interface states of the Ca doped BaTiO3 thin films were found to be higher than the pure BaTiO3 thin films.

Characteristics of LiNbO3 memory capacitors fabricated using a low thermal budget process

We investigated LiNbO3 metal ferroelectric semiconductor (MFS) capacitors because of the following advantages: a low interface trap density, a low interaction with Si substrate, and a large remanent polarization. Ferroelectric LiNbO3 thin films were grown directly on p-type Si(100) substrates for metal ferroelectric semiconductor field effect transistor (MFSFET) applications. Low temperature film growth and post rapid thermal anneal (RTA) treatments improved the leakage current of films while keeping other properties almost the same as high substrate temperature grown samples. We reduced the leakage current density of LiNbO3 films from 10−5 A/cm2 to 10−7 A/cm2 with RTA treatment. LiNbO3 MFS capacitors exhibited a breakdown electric field of greater than 500 kV/cm. RTA treatment above 600°C converted LiNbO3 films from amorphous to polycrystalline states with (012), (015), (022), and (023) planes. The polycrystalline LiNbO3 MFS capacitors illustrated the ferroelectric switching characteristics with a memory window ranging from 0.6 to 1.9 V. We obtained a remanent polarization of 2.74 μC/cm2 and a coercive field of 170 kV/cm using the LiNbO3 MFS capacitors.

Optical and electrical properties of BaTiO 3 thin films prepared by chemical solution deposition

Barium titanate sol was prepared using barium ethyl hexanoate and titanium isopropoxide. The sol was then spin coated on p-type single crystal silicon (100) wafers, stainless steel and fused silica substrates and annealed to give polycrystalline, transparent, and crack-free films. The surface morphology and structural properties of the films were studied using scanning electron microscopy and X-ray diffraction respectively. Crystalline phase could form only at an annealing temperature of 650°C and above. The effect of post deposition annealing on the optical and structural properties as well as on the band gap were analysed. Transmission spectra were recorded and from this, refractive index, extinction coefficient and thickness were calculated for films on fused silica annealed at different temperatures. The dispersion curve for the refractive index n of 650°C annealed film is fairly flat beyond 450 nm and rises sharply towards the shorter wavelength region, showing the typical shape of a dispersion curve near an interband transition. The present study indicates the validity of the DiDomenico model for the interband transition with a single electronic oscillator. The refractive indices lie in the range 1.75–2.5 for films annealed in the range 300–750°C. The electrical measurements were conducted on metal-ferroelectric-semiconductor (MFS) and metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant was 66 and 140 at 1 MHz for the MFS and MFM capacitors respectively. Debye type dispersion was observed for films on stainless steel substrates with an activation energy of about 0.34 eV. The low field ac conduction was found primarily due to hopping of electrons through the trap centres. The I-V characteristics of the MFS capacitor were found to be ohmic at low fields and space charge limited at high fields. I-V characteristics of the MFM capacitor showed a strange behaviour, linear dependence of current on voltage up to 10 6 V/m and V 5/2 dependence beyond 10 6 V/m.

Highly oriented ferroelectric CaBi2Nb2O9 thin films deposited on Si(100) by pulsed laser deposition

We report the successful deposition of highly c-axis oriented CaBi2Nb2O9 (CBN) thin films directly on p-type Si(100) substrates by pulsed laser deposition. The CBN thin films exhibited good structural, dielectric, and CBN/Si interface characteristics. The electrical measurements were conducted on CBN thin films in a metal–ferroelectric–semiconductor (MFS) capacitor configuration. The typical measured small signal dielectric constant and the dissipation factor at a frequency of 100 kHz were 80 and 0.051, respectively. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10−7A/cm2 at an applied electric field of 100 kV/cm. The capacitance–voltage measurements on MFS capacitors established good ferroelectric polarization switching characteristics.

Electrical Properties of Lead Lanthanum Titanate Thin-Film Capacitors Prepared by Sol-Gel Method

High-quality (Pb1-x Lax )Ti1-x /4O3 (x=0.05) [PLT] thin films were fabricated successfully by sol-gel processing onto Pt/Ti/SiO2/Si and p-Si substrates. The optimum route and the conditions for preparing homogeneous and crack-free thin films were systematically investigated. Ferroelectric perovskite phase was observed in the PLT thin films annealed at 600° C for 30 min. We studied the electrical properties of the PLT film capacitors with the metal-ferroelectric-metal (MFM) and the metal-ferroelectric-semiconductor (MFS) structure for use in ferroelectric memories. The dielectric constant and dissipation factor measured for MFM capacitor were 225 and 0.018 at 100 kHz, respectively. The remanent polarization (P r) and coercive field (E c) of the PLT film were 8.5 µC/cm2 and 110 kV/cm, respectively. Also the film with 600 nm thickness showed current density as low as 10-6 A/cm2 at the electric field of 200 kV/cm, which corresponds to the electric resistivity of ∼1012 (Ω·cm) and represents excellent insulating properties. The MFS capacitor showed ferroelectric switching properties in C-V characteristics and the memory window of the hysteresis loop was about 1 V in the operation of ±10 V.

Electrical Characterization of Ferroelectric Thin Films of Lithium Niobate on Silicon Substrates

ABSTRACTThin films (.1-.6 μm) of LiNbO3 have been deposited on silicon substrates by rf reactive sputtering. MFS (metal-ferroelectric-semiconductor) capacitor structures were created by a liftoff process which physically isolated small areas of LiNbO3. Standard MOS (metal-oxide-semiconductor) electrical characterization techniques were used to determine the resistivity and dielectric constant of the films. Short-circuit photocurrent measurements revealed both transient and steady state components attributed to a pyroelectric effect and a bulk photovoltaic effect respectively. The conduction processes in these films were examined and found to exhibit Frenkel-Poole characteristics. Ferroelectric switching at room temperature has also been observed in these films, however, the reversed orientation was not stable.

Characterization of sputtered thin films of barium strontium titanate on silicon substrates

Abstract Thin films of barium strontium titanate were r.f. sputter deposited at various temperatures, gas pressures, and gas compositions on both p-type and n-type (111) and (100) silicon substrates. Ellipsometry techniques were used to determine thickness and refractive index, while X-ray Bragg diffraction was used to determine the degree of crystallinity and orientation. SEM was used to reveal surface morphology and domain structure. Semi-transparent gold electrodes were evaporated on the films, to facilitate electrical characterization. Capacitance vs. voltage, current vs. voltage, and photocurrent measurements were used to characterize the MFS (metal ferroelectric semiconductor) capacitor structures. From these tests, dielectric constant, resistivity, pyroelectric coefficient, and breakdown field were determined.