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1.
Tantalum pentoxide films (13–260 nm) on p-type Si have been prepared by thermal oxidation at 673–873 K of rf sputtered Ta films and have been studied using Al–Ta2O5–Si capacitors. Both dielectric constant and refractive index were found to depend on the thickness of the Ta2O5 layers. Layers with a dielectric constant of 25–32 were obtained. A decreasing trend in the leakage current was found upon increasing oxidation temperature from 673 to 873 K. Leakage current density of (10−8 to 3×10−7) A cm−2 at 1 MV cm−1 effective field was achieved.  相似文献   

2.
The effect of various electrodes (Al, W, TiN) deposited by evaporation (Al) and sputtering (W, TiN) on the electrical characteristics of thermal thin film (15-35 nm) Ta2O5 capacitors has been investigated. The absolute level of leakage currents, breakdown fields, mechanism of conductivity, dielectric constant values are discussed in the terms of possible reactions between Ta2O5 and electrode material as well as electrode deposition process-induced defects acting as electrically active centers. The dielectric constant values are in the range 12-26 in dependence on both Ta2O5 thickness and gate material. The results show that during deposition of TiN and Al a reaction that worsens the properties of Ta2O5 occurs while there is not an indication for detectable reduction of Ta2O5 when top electrode is W, and the leakage current is 5-7 orders of magnitude lower as compared to Al and TiN-electroded capacitors. The high level of leakage current for TiN and Al gate capacitors are related to the radiation defects generated in Ta2O5 during sputtering of TiN, and damaged interface at the electrode due to a reaction between Al and Ta2O5, respectively. It is demonstrated that the quality of the top electrode affects the electrical characteristics of the capacitors and the sputtered W is found to be the best. The sputtered W gate provides Ta2O5 capacitors with a good quality: the current density <7 × 10−10 A/cm2 at 1 V (0.7 MV/cm, 15 nm thick Ta2O5). W deposition is not accompanied by an introduction of a detectable damage leading to a change of the properties of the initial as-grown Ta2O5 as in the case of TiN electrode. Damage introduced during TiN sputtering is responsible for current deterioration (high leakage current) and poor breakdown characteristics. It is concluded that the sputtered W top electrode is a good candidate as a top electrode of storage capacitors in dynamic random access memories giving a stable contact with Ta2O5, but sputtering technique is less suitable (favorable) for deposition of TiN as a metal electrode due to the introduction of radiation defects causing both deterioration of leakage current and poor breakdown characteristics.  相似文献   

3.
Characteristics of BaZrO3 (BZO) modified Sr0.8Bi2.2Ta2O9 (SBT) thin films fabricated by sol-gel method on HfO2 coated Si substrates have been investigated in a metal-ferroelectric-insulator-semiconductor (MFIS) structure for potential use in a ferroelectric field effect transistor (FeFET) type memory. MFIS structures consisting of pure SBT and doped with 5 and 7 mol% BZO exhibited memory windows of 0.81, 0.82 and 0.95 V with gate voltage sweeps between −5 and +5 V, respectively. Leakage current density levels of 10−8 A/cm2 for BZO doped SBT gate materials were observed and attributed to the metallic Bi on the surface as well as intrinsic defects and a porous film microstructure. The higher than expected leakage current is attributed to electron trapping/de-trapping, which reduces the data retention time and memory window. Further process improvements are expected to enhance the electronic properties of doped SBT for FeFET.  相似文献   

4.
Electrical properties of mixed HfO2-Ta2O5 films (10;15 nm) deposited by rf sputtering on Si have been studied from the view point of their applications as high-k layers, by standard capacitance-voltage and temperature dependent current-voltage characteristics. The effect of HfO2 addition to the Ta2O5 is thickness dependent and the thicker layers exhibit advantages over the pure Ta2O5 (higher dielectric constant, enhanced charge storage density and improved interface quality). The process of HfO2 and Ta2O5 mixing introduces negative oxide charge, tends to creates shallow bulk traps and modifies the dominant conduction mechanisms in the stack capacitors as compared to the Ta2O5-based one (a contribution of tunneling processes through traps located below the conduction band of mixed layers to the leakage current in the HfO2-Ta2O5 stacks is observed). The traps involved in both Poole-Frenkel and tunneling processes are identified.  相似文献   

5.
Tantalum pentoxide (Ta2O5) deposited by pulsed DC magnetron sputtering technique as the gate dielectric for 4H-SiC based metal-insulator-semiconductor (MIS) structure has been investigated. A rectifying current-voltage characteristic was observed, with the injection of current occurred when a positive DC bias was applied to the gate electrode with respect to the n type 4H-SiC substrate. This undesirable behavior is attributed to the relatively small band gap of Ta2O5 of around 4.3 eV, resulting in a small band offset between the 4H-SiC and Ta2O5. To overcome this problem, a thin thermal silicon oxide layer was introduced between Ta2O5 and 4H-SiC. This has substantially reduced the leakage current through the MIS structure. Further improvement was obtained by annealing the Ta2O5 at 900 °C in oxygen. The annealing has also reduced the effective charge in the dielectric film, as deduced from high frequency C-V measurements of the Ta2O5/SiO2/4H-SiC capacitors.  相似文献   

6.
The influence of the rapid thermal annealing (RTA) in vacuum at 1000 °C on the leakage current characteristics and conduction mechanisms in thermal Ta2O5 (7-40 nm) on Si has been studied. It was established that the effect of RTA depends on both the initial parameters of the films (defined by the oxidation temperature and film thickness) and annealing time (15-60 s). The RTA tends to change the distribution and the density of the traps in stack, and this reflects on the dielectric and leakage properties. The thinner the film and the poorer the oxidation, the more susceptible the layer to heating. The short (15 s) annealing is effective in improving the leakage characteristics of poorly oxidized samples. The RTA effect, however, is rather deleterious than beneficial, for the thinner layers with good oxygen stoichiometry. RTA modifies the conduction mechanism of Ta2O5 films only in the high-field region. The annealing time has strong impact on the appearance of a certain type of reactions upon annealing resulting to variation of the ratio between donors and traps into Ta2O5, causing different degree of compensation, and consequently to domination of one of the two mechanisms at high fields (Schottky emission or Poole-Frenkel effect). Trends associated with simultaneous action of annealing and generation of traps during RTA processing, and respectively the domination of one of them, are discussed.  相似文献   

7.
The stress-induced leakage current in Hf-doped Ta2O5 layers (7; 10 nm) under constant voltage stress at gate injection was investigated in order to assess the mechanisms of conduction, the traps involved and the effect of Hf doping. The amount of Hf is found to affect the conduction mechanisms, the temperature dependence of the leakage current and the current response to the stress. A significant leakage current increase is observed only when the stress voltage and/or stress time exceed the corresponding threshold values, where the charge trapping at the pre-existing traps dominates below and defect generation above these threshold values. The energy levels of the traps responsible for the current transport are estimated. The stress effect on dominant conduction mechanisms appears quite weak, and the nature of the traps controlling the current transport before and after the stress seems to be nearly identical. The results indicate that the constant voltage stress affects the pre-existing traps in Hf-doped Ta2O5 and modifies their parameters, but there is no evidence for stress-induced generation of traps with completely new nature different from oxygen-vacancy related defects.  相似文献   

8.
The conduction mechanisms and the microstructure of rf sputtered Ta2O5 on Si, before and after oxygen annealing at high temperatures (873, 1123 K; 30 min) have been investigated. The as-deposited and annealed at 873 K layers are amorphous whereas crystalline Ta2O5 (orthorhombic β-Ta2O5 phase) was obtained after O2 treatment at 1123 K. The results (electrical, X-ray diffraction, transmission electron microscopy) reveal the formation of an interfacial ultrathin SiO2 layer under all technological regimes used. The higher (493 K) substrate temperature during deposition stimulates the formation of amorphous rather than crystalline SiO2. It is found that the oxygen heating significantly reduces the oxide charge (Qf<1010 cm−2) and improves the breakdown characteristics (the effect is more pronounced for the higher annealing temperature). It is accompanied by an increase of the effective dielectric constant (up to 37 after 1123 K treatment). It is established that the influence of the oxygen treatment on the leakage current is different depending on the film thickness, namely: a beneficial effect for the thinner and a deterioration of leakage characteristics for thicker (80 nm) films. A leakage current density as low as 10−7 A/cm2 at 1 MV/cm applied field for 26 nm annealed layers has been obtained. The current reduction is considered to be due to a removal by annealing of certain structural nonperfections present in the initial layers. Generally, the results are discussed in terms of simultaneous action of two opposite and competing processes taking place at high temperatures––a real annealing of defects and an appearance of a crystal phase and/or a neutral traps generation. The contribution of the neutral traps also is involved to explain the observed weaker charge trapping in the as-fabricated films compared to the annealed ones.The conduction mechanism of the as-deposited films is found to be of Poole–Frenkel (PF) type for a wide range of applied fields. A change of the conduction mechanism for the annealed films at medium fields (0.8–1.3 MV/cm) is established. This transition from PF process to the Schottky emission limited current is explained with an annealing of bulk traps (oxygen vacancies and nonperfect bonds). It is concluded that the dominant conduction mechanism in the intermediate fields can be effectively controlled by appropriate technological steps.  相似文献   

9.
A Ge-stabilized tetragonal ZrO2 (t-ZrO2) film with permittivity (κ) of 36.2 was formed by depositing a ZrO2/Ge/ZrO2 laminate and a subsequent annealing at 600 °C, which is a more reliable approach to control the incorporated amount of Ge in ZrO2. On Si substrates, with thin SiON as an interfacial layer, the SiON/t-ZrO2 gate stack with equivalent oxide thickness (EOT) of 1.75 nm shows tiny amount of hysteresis and negligible frequency dispersion in capacitance-voltage (C-V) characteristics. By passivating leaky channels derived from grain boundaries with NH3 plasma, good leakage current of 4.8 × 10−8 A/cm2 at Vg = Vfb − 1 V is achieved and desirable reliability confirmed by positive bias temperature instability (PBTI) test is also obtained.  相似文献   

10.
In this study, high-pressure oxygen (O2 and O2 + UV light) technologies were employed to effectively improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this work, 13 nm HfO2 thin films were deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 °C were performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO2 film after O2 and O2 + UV light treatments can be improved from 3.12 × 10−6 A/cm2 to 6.27 × 10−7 and 1.3 × 10−8 A/cm2 at |Vg| = 3 V. The proposed low-temperature and high pressure O2 or O2 + UV light treatment for improving high-k dielectric films is applicable for the future flexible electronics.  相似文献   

11.
Normally-off GaN-MOSFETs with Al2O3 gate dielectric have been fabricated and characterized. The Al2O3 layer is deposited by ALD and annealed under various temperatures. The saturation drain current of 330 mA/mm and the maximum transconductance of 32 mS/mm in the saturation region are not significantly modified after annealing. The subthreshold slope and the low-field mobility value are improved from 642 to 347 mV/dec and from 50 to 55 cm2 V−1 s−1, respectively. The ID-VG curve shows hysteresis due to oxide trapped charge in the Al2O3 before annealing. The amount of hysteresis reduces with the increase of annealing temperature up to 750 °C. The Al2O3 layer starts to crystallize at a temperature of 850 °C and its insulating property deteriorates.  相似文献   

12.
New ZrO2/Al2O3/ZrO2 (ZAZ) dielectric film was successfully developed for DRAM capacitor dielectrics of 60 nm and below technologies. ZAZ dielectric film grown by ALD has a mixture structure of crystalline phase ZrO2 and amorphous phase Al2O3 in order to optimize dielectric properties. ZAZ TIT capacitor showed small Tox.eq of 8.5 Å and a low leakage current density of 0.35 fA/cell, which meet leakage current criteria of 0.5 fA/cell for mass production. ZAZ TIT capacitor showed a smaller cap leak fail bit than HAH capacitor and stable leakage current up to 550 °C anneal. TDDB (time dependent dielectric breakdown) behavior reliably satisfied the 10-year lifetime criteria within operation voltage range.  相似文献   

13.
The sintering process of semiconducting Y-doped BaTiO3 ceramics added with BaB2O4 as low temperature sintering aid were investigated. When the low temperature sintering aid BaB2O4 added Y-doped BaTiO3 ceramics prepared by Sol-Gel method, the sintering temperature of BaTiO3-based ceramics would be greatly decreased, and also widen sintering range. Y-doped BaTiO3 ceramics with BaB2O4 addition can be obtained at 1050 °C. Ceramics samples with room temperature resistivity 60-80 Ω cm, ratio of the maximum resistivity to minimum resistance (Rmax/Rmin) 104 and temperature coefficient of resistivity (α) 10%/°C were obtained.  相似文献   

14.
Rare earth oxides (REOs) have lately received extensive attention in relation to the continuous scaling down of non-volatile memories (NVMs). In particular, La2O3 films are promising for integration into future NVMs because they are expected to crystallize above 400 °C in the hexagonal phase (h-La2O3) which has a higher κ value than the cubic phase (c-La2O3) in which most of REOs crystallize. In this work, La2O3 films are grown on Si by atomic layer deposition using La(C5H5)3 and H2O. Within the framework of the h-La2O3 formation, we systematically study the crystallographic evolution of La2O3 films versus annealing temperature (200-600 °C) by Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction (GIXRD). As-grown films are chemically unstable in air since a rapid transformation into monoclinic LaO(OH) and hexagonal La(OH)3 occurs. Vacuum annealing of sufficiently thick (>100 nm) La(OH)3 layers induces clear changes in FTIR and GIXRD spectra: c-La2O3 gradually forms in the 300-500 °C range while annealing at 600 °C generates h-La2O3 which exhibits, as inferred from our electrical data, a desirable κ ∼ 27. A quick transformation from h-La2O3 into La(OH)3 occurs due to H2O absorption, indicating that the annealed films are chemically unstable. This study extends our recent work on the h-La2O3 formation.  相似文献   

15.
TaYOx-based metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated. Ultra-thin TaYOx films in the thickness range of 15-30 nm (EOT ∼ 2.4-4.7 nm) were deposited on Au/SiO2 (100 nm)/Si (100) structures by rf-magnetron co-sputtering of Ta2O5 and Y2O3 targets. TaYOx layers were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) to examine the composition and crystallinity. An atomic percentage of Ta:Y = 58.32:41.67 was confirmed from the EDX analysis while XRD revealed an amorphous phase (up to 500 °C) during rapid thermal annealing. Besides, a high capacitance density of ∼3.7-5.4 fF/μm2 at 10 kHz (εr ∼ 21), a low value of VCC (voltage coefficients of capacitance, α and β) have been achieved. Also, a highly stable temperature coefficient of capacitance, TCC has been obtained. Capacitance degradation phenomena in TaYOx-based MIM capacitors under constant current stressing (CCS at 20 nA) have been studied. It is observed that degradation depends strongly on the dielectric thickness and a dielectric breakdown voltage of 3-5 MV/cm was found for TaYOx films. The maximum energy storage density was estimated to be ∼5.69 J/cm3. Post deposition annealing (PDA) in O2 ambient at 400 °C has been performed and further improvement in device reliability and electrical performances has been achieved.  相似文献   

16.
In this article, the conduction mechanisms of metal-oxide-semiconductor with vacuum annealed Lanthana (La2O3) oxide film are investigated. Lanthana films with thicknesses of 3.5, 4.7, and 11 nm were deposited by E-beam evaporation on n-Si (100), and annealed at various temperatures (300-500 °C) in ultra-high vacuum (10−10-10−9 Torr) for 90 min. From the measurement of spectroscopic ellipsometry, it is found that film thickness is increased with annealing temperature, which would be cause of flat-band voltage shift (ΔVFB) due to the growth of interfacial layer. From the capacitance measurement, it is found that ΔVFB of the film is reduced by post-deposition anneal (PDA) compared to that of as-deposited film, but increase again at high temperature annealing, especially in the case of thin film (3.5 nm). From the applied voltage and temperature dependence of the leakage current of the film, with different gate electrode materials (Ag, Al, and Pt), it is shown that the leakage currents are associated with ohmic and Poole-Frenkel (P-F) conductions when flat-band voltage (VFB) is less than zero, and ohmic and Space-Charge-Limited Current (SCLC) conductions when VFB is greater than zero. The dielectric constants obtained from P-F conduction for Al gate electrode case is found to be 11.6, which is consistent with the C-V result 11.9. Barrier height of trap potential well is found to be 0.24 eV from P-F conduction. Based on SCLC theory, leakage currents of 3.5 and 11 nm films with different PDA temperatures are explained in terms of oxide trap density.  相似文献   

17.
ZrO2 thin films were deposited by the atomic layer deposition process on Si substrates using tetrakis(N,N′-dimethylacetamidinate) zirconium (Zr-AMD) as a Zr precursor and H2O as an oxidizing agent. Tetrakis (ethylmethylamino) zirconium (TEMA-Zr) was also evaluated for a comparative study. Physical properties of ALD-derived ZrO2 thin films were studied using ellipsometry, grazing incidence XRD (GI-XRD), high resolution TEM (HRTEM), and atomic force microscopy (AFM). The ZrO2 deposited using Zr-AMD showed a better thermal stability at high substrate temperature (>300 °C) compared to that using TEMA-Zr. GI-XRD analysis reveals that after 700 °C anneal both ZrO2 films enter tetragonal phase. The electrical properties of N2-annealed ZrO2 film using Zr-AMD exhibit an EOT of 1.2 nm with leakage current density as low as 2 × 10−3 A/cm2 (@Vfb−1 V). The new Zr amidinate is a promising ALD precursor for high-k dielectric applications.  相似文献   

18.
Metal-multiferroic (La-substituted BiFeO3)-insulator (CeO2)-semiconductor (MFIS) capacitors has been fabricated. The crystalline phase and amount of La3+ substitution at Bi-site were investigated by XRD and XPS in the postannealing temperature range from 500 to 700 °C, respectively. The microstructure and interfacial layer between CeO2 and Si substrate were characterized by HRTEM. The memory windows as functions of insulator film thickness and DC power for La were measured. The maximum memory window is about 1.9 V under ±6 V applied voltage. The ferroelectric polarization increases with increasing substitution amount. The morphologies of La-substituted BiFeO3 films were also studied by AFM.  相似文献   

19.
Yttrium was deposited on the chemical oxide of Si and annealed under vacuum to control the interface for the formation of Y2O3 as an insulating barrier to construct a metal-ferroelectric-insulator-semiconductor structure. Two different pre-annealing temperatures of 600 and 700 °C were chosen to investigate the effect of the interface state formed after the pre-annealing step on the successive formation of Y2O3 insulator and Nd2Ti2O7 (NTO) ferroelectric layer through annealing under an oxygen atmosphere at 800 °C. Pre-anneal treatments of Y-metal/chemical-SiO2/Si at 600 and 700 °C induced a formation of Y2O3 and Y-silicate, respectively. The difference in the pre-anneal temperature induced almost no change in the electrical properties of the Y2O3/interface/Si system, but degraded properties were observed in the NTO/Y2O3/interface/Si system pre-annealed at 600 °C when compared with the sample pre-annealed at 700 °C. C-V characteristics of the NTO/Y2O3/Si structured system showed a clockwise direction of hysteresis, and this gap could be used as a memory window for a ferroelectric-gate. A smaller hysteric gap and electrical breakdown values were observed in the NTO/Y2O3/Si system pre-annealed at 600 °C, and this was due to an unintentional distribution of the applied field from the presence of an interfacial layer containing Y-silicate and SiO2 phases.  相似文献   

20.
The temperature dependence of the dielectric properties of high Q polymer-based composites was discussed in terms of microstructural differences with various filler contents. Liquid coatable high Q polymer-based composites with 3-4× improvement in dielectric constant and precisely controlled temperature coefficient of capacitance (TCC) were developed with Ta2O5 as the inorganic filler. The base polymer showed a negative TCC of −250 ppm/°C from room temperature to 125 °C. Measurement of TCC with samples containing Ta2O5 greater than 30 vol.% showed TCC of ±50 ppm/°C with moderate capacitance density, whereas no detectable improvement in the TCC was observed in samples having 20 vol.% Ta2O5. The electron micrographs of this low filler content sample gave a clear indication of clustering, i.e. particle agglomeration. The homogeneity of the particle distribution was more pronounced in the sample with 40 vol.% Ta2O5.  相似文献   

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