High Breakdown Electric Field Research Articles

High-Rate Homoepitaxial Growth of Heavily Boron-Doped Diamond (100) Films By Microwave Plasma-Enhanced Chemical Vapor Deposition Using High Microwave Power Density

Diamond is expected as a next-generation semiconductor material for high-power devices because of its high breakdown electric field, mobility, and thermal conductivity. For the power devices with high current operation, vertical structures are effective because the large contact area is easily obtained by trench structures in the same way as silicon and silicon carbide power devices. The low resistivity diamond single-crystal substrates are required to fabricate the diamond vertical power devices and are realized by heavy boron doping. The highest growth rate of heavily boron-doped ([B]film > 1020 atoms/cm3) diamond films obtained by microwave plasma-enhanced chemical vapor deposition (MPECVD) is 6 μm/h [1]. The higher growth rate is required for manufacturing cost reduction of the low resistivity diamond substrates. However, the higher the boron concentration is, the lower the growth rate of the diamond films becomes [1]. It is known that there are mainly two methods for increasing the growth rate of the diamond films. One is a nitrogen addition to the plasma. However, incorporated nitrogen into diamond acts as a donor, which is compensator for boron-doped diamond [2]. The other is high density of the microwave power input into the plasma. Therefore, we tried to change the shape of a diamond substrate holder for MPECVD to improve the growth rate by increasing the power density near the surface of substrate. Figure 1 shows the plasma states of (a) the conventional substrate holder and (b) the improved substrate holder. The improved substrate holder has a shallower bottom than the conventional one. In the case of the improved substrate holder, the top of the diamond substrate is higher than that of the holder, as shown in Fig.1(b). As a result, the diamond growth rate and incorporation of boron atoms into the diamond film are enhanced at the same time because the electric field is concentrated at the top surface of the diamond substrate and the radical density on the diamond surface increases. High-pressure, high-temperature (HPHT) synthetic Ib(100) single-crystal diamonds were used as substrates for the homoepitaxial diamond growth by MPECVD with a spherical resonator structure (Arios Inc. in Japan). Before the CVD growth, the diamond substrates were treated with HF diluted with H2O for 15 min. Next, the substrates were heated in 2:1 mixture of H2O2 and H2SO4 at 400°C for 15 min. The growth was carried out using CH4 and B(CH3)3 diluted with H2. The microwave power, the total pressure and the methane concentration were maintained at 900 W, 50 kPa and 2.4 %, respectively. The boron/carbon (B/C) ratios in the gas phase were fixed at 14,000 ppm for the conventional holder and 20,000 ppm for the improved substrate holder, respectively. The growth of the heavily boron-doped diamond films was conducted for two hours in the above conditions. After the growth, the surface morphologies of the heavily boron-doped diamond films were observed by optical microscopy (OM). The resistivities of the films were measured by a van der Pauw contact configuration and the growth rates were estimated by the micrometer. Figure 2 shows the OM images of typical surface morphologies of the heavily boron-doped diamond films grown on diamond (100) substrates by (a) the conventional substrate holder and (b) the improved substrate holder. Although the diamond film grown by the conventional substrate holder had some non-epitaxial crystallites with density of 1.6 × 104 cm-2, which degrade the diamond device performances, the diamond film grown by the improved substrate holder had no non-epitaxial crystallites. The resistivities of the films were 3.3 × 10-2 Ωcm for the improved substrate holder and 2.3 × 10-2 Ωcm for the conventional substrate holder, respectively. The boron concentrations in these films were 1~3 × 1020 cm-3, which is estimated from the growth condition. The growth rates were 29.5 μm/h for the improved substrate holder and 13.0 μm/h for the conventional substrate holder, respectively. The growth rate of 29.5 μm/h is the highest growth rate for heavily boron-doped ([B]film> 1020 cm-3) diamond films. Acknowledgements This work was partially supported by Adaptable and Seamless Technology Transfer Program through Target-driven R&D, JST, and Kanazawa University SAKIGAKE Project.

Enhanced energy-storage performance of 0.94NBT-0.06BT thin films induced by a Pb0.8La0.1Ca0.1Ti0.975O3 seed layer

0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 ferroelectric thin films with and without the Pb0.8La0.1Ca0.1Ti0.975O3 seed layer were deposited on platinum-buffered silicon substrates by using Sol–Gel process. The influence of Pb0.8La0.1Ca0.1Ti0.975O3 seed layer and annealing temperatures on the microstructures, ferroelectric properties and energy-storage performances of the as-prepared films were investigated in details. The low annealing temperature and Pb0.8La0.1Ca0.1Ti0.975O3 seed layer could improve the values of electric break-down field strength and Pmax-Pr, which play a vital role for high recoverable energy-storage density. Owing to the high electric break-down field strength value of 3310kV/cm, a large recoverable energy density of W=17.2J/cm3 and a high energy efficiency of η=74.3% were obtained for the 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 thin film with the Pb0.8La0.1Ca0.1Ti0.975O3 seed layer, which was annealed at 450°C.

(Invited) Development of β-Ga2O3 Materials

β-Ga2O3 has attracted significant recent attention for its large bandgap of 4.8 eV which leads to a high breakdown electric field, predicted to be 8 MV/cm. With a predicted maximum bulk electron mobility of 300 cm2/Vs, β-Ga2O3 yields a Baliga figure of merit (BFOM) that is higher than that of 4H-SiC and GaN. β-Ga2O3 has a monoclinic crystal structure (usually represented with the b-axis as the unique axis) with strong anisotropy in physical properties. The crystal cleaves easily on the (100) and (201) planes. MBE growth on cleavage planes yields low growth rates due to a strong propensity for Ga loss via suboxides [M.-Y. Tsai et al., J. Vac Sci. Tech. A 28, 354 (2010).]. Growth on non-cleavage planes, such as (010), however, yields high growth rates [K. Sasaki et al., J. Cryst. Growth 378, 591 (2013).]. In this presentation, we review our work on development of growth of β-Ga2O3 (010) by plasma-assisted MBE. We present the development of high temperature homoepitaxial growth of β-Ga2O3 (010) and preliminary Sn doping [H. Okumura et al., Appl. Phys. Express 7, 095501 (2014)]; the development of coherent β-(AlxGa1-x)2O3/Ga2O3 heterostructures [Kaun et al., J. Vac. Sci. Tech. 33, 041508 (2015)]; and viable RIE and ICP etch processes [J. Hogan et al., in preparation].

Low Interface Trap Density and High Breakdown Electric Field SiN Films on GaN Formed by Plasma Pretreatment Using Microwave-Excited Plasma-Enhanced Chemical Vapor Deposition

Low Interface Trap Density and High Breakdown Electric Field SiN Films on GaN Formed by Plasma Pretreatment Using Microwave-Excited Plasma-Enhanced Chemical Vapor Deposition

Performance of ultra‐thin HfO2‐based MIM devices after oxygen modulation and post‐metallization annealing in N2

In this work, we discuss the electrical characteristics of metal–insulator–metal (MIM) structures based on ultra‐thin hafnium oxides whose stoichiometry have been modified and a thermal treatment after gate metallization has also been applied. Here, we show that the current–voltage characteristics are improved for the annealed samples in terms of lower gate leakage current densities and higher breakdown electric fields. In addition, the role of the modulation in the oxygen concentration for HfO2 on the MIM's current–voltage, capacitance–voltage, and resistive switching characteristics is also addressed. From these data, a trade‐off between current–voltage characteristics and basic memory performance is clearly seen, thus highlighting the importance of combining oxygen modulation and/or post‐metallization annealing in HfO2‐based MIM structures. Finally, the resistive switching effect is shown in the bipolar mode for some MIM structures and the dominant carrier conduction mechanism (just before the SET condition) is also obtained and related to Poole–Frenkel conduction.

Characterization of Leakage and Reliability of SiN<sub><italic>x</italic></sub> Gate Dielectric by Low-Pressure Chemical Vapor Deposition for GaN-based MIS-HEMTs

In this paper, we systematically investigated the leakage and breakdown mechanisms of the low-pressure chemical vapor deposition (LPCVD) silicon nitride thin film deposited on AlGaN/GaN heterostructures. The LPCVD-SiN x gate dielectric exhibits low leakage and high breakdown electric field. The dominant mechanism of the leakage current through LPCVD-SiN x gate dielectric is identified to be Poole–Frenkel emission at low electric field and Fowler–Nordheim tunneling at high electric field. Both electric-field-accelerated and temperature-accelerated time-dependent dielectric breakdown of the LPCVD-SiN x gate dielectric were also investigated.

Large electrocaloric effect in lead-free K0.5Na0.5NbO3-SrTiO3 ceramics

The electrocaloric effect (ECE), i.e., the adiabatic temperature change ΔTEC, of the lead-free relaxor ferroelectric 0.85K0.5Na0.5NbO3-0.15SrTiO3 (KNN-STO) ceramics is investigated. The ECE data obtained by a direct method show the existence of a large ECE near the temperature of the dielectric permittivity maximum. Due to the high break-down electric field, a large ΔTEC exceeding 1.2 K at 300 K and 1.9 K at 340 K was observed at 159 kV/cm in a broad temperature range of 80 K. Such a high ECE response near the room temperature is comparable to that found in lead-based ceramic materials, thus making KNN-STO a strong candidate to replace lead-based materials in future electrocaloric applications.

Effect of kaolinite-doping on the microstructure and the dielectric properties of CaCu3Ti4O12 ceramics

Commercial kaolinite was employed to improve the dielectric property of CaCu3Ti4O12 (CCTO), and the CCTO–xwt% kaolinite samples (x=0, 5, 10, 20) were synthesized by a solid state method. X-ray diffraction results indicated that no foreign ions enter the crystal lattice of CCTO, but CuO and CaTiO3 exist as second phases in grain boundary. Scanning electron microscope measurements showed that the size of grain decreased with increasing doping content except for x=5% sample. Kaolinite additive can inhibit the grain growth, which is beneficial to lower the dielectric loss of a CaCu3Ti4O12 (CCTO) system (mostly tanδ<0.05, when x=20). The current–voltage (or J–E) characteristics were investigated and found that the x=5% sample exhibited an extremely high breakdown electric field of 8000V/cm.

Fulfilling the Promise of High-Temperature Operation with Silicon Carbide Devices: Eliminating bulky thermal-management systems with SJTs

Electronics operating at high temperatures are expected to revolutionize key industries in ways not yet imagined. It will allow aerospace engine applications, actuators and downhole electronics, and vehicle power systems to be squeezed into significantly smaller spaces through reduction or elimination of bulky thermal-management systems. Silicon carbide (SiC) offers great potential for the realization of high-temperature power devices because of its attractive electrical properties, such as wide bandgap, high breakdown electric field, and high thermal conductivity. However, many device structures in SiC are not suitable for use at high temperatures because they are not able to fully exploit these properties to deliver lowleakage currents and superior long-term reliability. In contrast, SiC junction transistors (SJTs) and optimized junction barrier Schottky (JBS) rectifiers have now been demonstrated with superior high-temperature performance due to their intrinsic advantages stemming from these device structures. This article surveys important physical phenomenon that limit high-temperature operation of SiC power devices, and presents experimental results from GeneSiC of higher temperature SiC power device operation.

From Nanoparticles to Nanowires of GaN with Different Hydrogen Gas Flow Rates by PDC-PECVD

III-V family semiconductors have received considerable attention for microelectronic and optoelectronic applications. In particular, GaN nanostructures have a huge number of applications due to its wide and direct band gap, high melting point and high electrical breakdown field. Wurtzite structure of GaN nanoparticles and nanowires were synthesized using different hydrogen gas flow rate of 0, 3 and 7sccm (standard cubic centimetres per minute) via pulsed direct current plasma enhanced chemical vapor deposition (PDC-PECVD) at low temperature, 650°C. GaN nanostructures including nanowires and nanoparticles were grown using gallium atoms and nitrogen plasma on Si (111) substrates. Characterizations of GaN nanostructures were carried out using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and field emission electron microscopy (FE-SEM). Morphology of the grown GaN nanostructures changed from nanoparticles to nanowires with increasing the hydrogen gas flow rates. XRD results demonstrate that lattice constants ratio of a/c of hexagonal structure and gallium/nitrogen ratio in the synthesized GaN nanostructures decreased with increasing hydrogen flow rates. GaN nanoparticles and nanowires were grown on Si (111) with average diameters of 45nm and 25nm, respectively. The results show that the hydrogen plasma can significantly affects on morphology and lattice parameters of GaN nanostructures by low temperature PECVD method.

AlGaN channel MIS-HEMTs with a very high breakdown electric field and excellent high-temperature performance

AlGaN channel MIS-HEMTs with a very high breakdown electric field and excellent high-temperature performance

Fully Solution-Processed Low-Voltage Aqueous In2O3 Thin-Film Transistors Using an Ultrathin ZrOx Dielectric

We reported here "aqueous-route" fabrication of In2O3 thin-film transistors (TFTs) using an ultrathin solution-processed ZrOx dielectric thin film. The formation and properties of In2O3 thin films under various annealing temperatures were intensively examined by thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. The solution-processed ZrOx thin film followed by sequential UV/ozone treatment and low-temperature thermal-annealing processes showed an amorphous structure, a low leakage-current density (∼1 × 10(-9) A/cm(2) at 2 MV/cm), and a high breakdown electric field (∼7.2 MV/cm). On the basis of its implementation as the gate insulator, the In2O3 TFTs based on ZrOx annealed at 250 °C exhibit an on/off current ratio larger than 10(7), a field-effect mobility of 23.6 cm(2)/V·s, a subthreshold swing of 90 mV/decade, a threshold voltage of 0.13 V, and high stability. These promising properties were obtained at a low operating voltage of 1.5 V. These results suggest that "aqueous-route" In2O3 TFTs based on a solution-processed ZrOx dielectric could potentially be used for low-cost, low-temperature-processing, high-performance, and flexible devices.

Electrical properties of (Zr,Ti)0.85(Ca,Sr)0.15O1.85 thin film grown on Pt/Ti/SiO2/Si substrate using RF magnetron sputtering

Crystalline (Zr,Ti)0.85(Ca,Sr)0.15O1.85 (ZTCS) films were grown on a Pt/Ti/SiO2/Si substrate at various temperatures by using rf-magnetron sputtering. The ZTCS films had a cubic stabilized zirconia structure. The dielectric constant (k) of the ZTCS film grown at 300°C was approximately 30.5 with a low tanδ value of 0.007 at 100kHz. Further, this film exhibited a similar k value of 30.4 and a high quality factor of 225 at 1.0GHz. Moreover, it showed a high capacitance density of 290nF/cm2 with a small TCC of −60.7ppm/°C at 100kHz. A low leakage current (1.4×10−8A/cm2 at 1.5MV/cm) with a high breakdown electric field (1.85MV/cm) was also observed in this film; the leakage current of this film was explained by Schottky emission. Therefore, it can be concluded that ZTCS films grown at low temperatures (≤300°C) are good candidates for use as embedded capacitor in printed circuit boards.

SIC: AN ADVANCED SEMICONDCTOR MATERIAL FOR POWER DEVICES

Silicon carbide (SiC) is a wide band gap material that shows great promise in high-power and high temperature electronics applications because of its high thermalconductivity and high breakdown electrical field. This paper describes how the outstanding physical andelectronic properties ofSiC permit the fabrication of devices that can operate athigher temperature and power levels than devices fabricated from other material such as silicon orGaAs. In spite of, recent electronics depends primarily upon Silicon based devices;this material is not capable of handling many greater requirements. Devices which operate at high frequency, at high power levels and are to be used in seriousenvironments at high temperatures and high radiation levels required other materialswith wider band gaps than that of silicon. Many space and ground based application rather than satellite applications also have a requirement for wide band gap materials. SiC also has great strength for high power and frequency operation due to a high saturated drift velocity. The Wide band gap permit for unusual optoelectronic applications that include blue light emitting diodes and ultraviolet photo detectors New areas involving gas sensing and RF applications offer significant promise. Overall, the properties of SiC make it one of the best prospects for extending the capabilities and operational regimes of the current semiconductor device technology.

Transition of the polarization switching from extrinsic to intrinsic in the ultrathin polyvinylidene fluoride homopolymer films

Polyvinylidene fluoride homopolymer thin films have been prepared by the Langmuir-Blodgett technique, and their electrical properties have comprehensively been studied. The polyvinylidene fluoride homopolymer films show better ferroelectricity with higher polarization and higher breakdown electric field than that of the poly(vinylidene fluoride-trifluoroethylene) copolymer films. Inspection on the thickness dependence of the coercive field of the polyvinylidene fluoride films suggests an extrinsic polarization switching occurs in the thickness range from 200 to 45 nm, and a non-extrinsic switching is observed in the range between 45 and 11 nm, which is ascribed to the transition range from extrinsic to intrinsic switching.

Comparison of high-κ Nd2O3 and NdTiO3 dielectrics deposited on polycrystalline silicon substrates

High-κ Nd2O3 and NdTiO3 films deposited on polycrystalline silicon treated at various post-rapid thermal annealing temperatures were fabricated as high-κ gate dielectrics. The NdTiO3 samples demonstrated a higher effective dielectric constant, lower leakage current, higher breakdown electric field, smaller gate voltage shift, and lower electron trapping rate than the high-κ Nd2O3 polyoxide dielectric samples. Annealing effects were analyzed using electrical measurements and multiple material analysis techniques included X-ray diffraction and atomic force microscopy. Incorporating Ti content into Nd2O3 dielectrics resulted in noticeable improvements in electrical performance and material quality. Results indicate that NdTiO3 dielectrics show promise for future high-κ dielectric electronic device applications.

A review of GaN-based optoelectronic devices on silicon substrate

Group III-nitride material system possesses some unique properties, such as large spectrum coverage from infrared to deep ultraviolet, wide energy band gap, high electron saturation velocity, high electrical breakdown field, and strong polarization effect, which enables the big family has a very wide application range from optoelectronic to power electronic area. Furthermore, the successful growth of GaN-related III-nitride material on large size silicon substrate enable the above applications easily realize the commercialization, because of the cost-effective device fabrication on the platform of Si-based integrated circuits. In this article, the progress and development of the GaN-based materials and light-emitting diodes grown on Si substrate were summarized, in which some key issues regarding to the material growth and device fabrication were reviewed.

Improved Dielectric and Nonlinear Electrical Properties of Fine‐Grained CaCu3Ti4O12 Ceramics Prepared by a Glycine‐Nitrate Process

Pure CaCu3Ti4O12 was successfully prepared by a glycine‐nitrate process using a relatively low calcination temperature and short reaction time of 760°C for 4 h. Fine‐grained CaCu3Ti4O12 ceramics with dense microstructure and small grain size were obtained after sintering for 1 h. The nonlinear coefficient of a fine‐grained CaCu3Ti4O12 ceramic calculated in the range 1–10 mA/cm2 was found to be very high of ~16.39 with high breakdown electric field strength of 1.46 × 104 V/cm. This fine‐grained CaCu3Ti4O12 ceramic also exhibited a very low loss tangent of 0.017 at 20°C with temperature stability over the range −55°C to 85°C. The grain growth rate of the CaCu3Ti4O12 ceramics was found to be very fast after increasing the sintering time from 1.5 to 3 h, leading to formation of a coarse‐grained CaCu3Ti4O12 ceramic with grain size of about 100–200 μm. The dielectric permittivity of this coarse‐grained ceramic was found to be as high as 1.03 × 105 with a low loss tangent of 0.054.

Electronic transport and device prospects of monolayer molybdenum disulphide grown by chemical vapour deposition

Layered transition metal dichalcogenides display a wide range of attractive physical and chemical properties and are potentially important for various device applications. Here we report the electronic transport and device properties of monolayer molybdenum disulphide grown by chemical vapour deposition. We show that these devices have the potential to suppress short channel effects and have high critical breakdown electric field. However, our study reveals that the electronic properties of these devices are at present severely limited by the presence of a significant amount of band tail trapping states. Through capacitance and ac conductance measurements, we systematically quantify the density-of-states and response time of these states. Because of the large amount of trapped charges, the measured effective mobility also leads to a large underestimation of the true band mobility and the potential of the material. Continual engineering efforts on improving the sample quality are needed for its potential applications.

A review on the dielectric materials for high energy-storage application

With the fast development of the power electronics, dielectric materials with high energy-storage density, low loss, and good temperature stability are eagerly desired for the potential application in advanced pulsed capacitors. Based on the physical principals, the materials with higher saturated polarization, smaller remnant polarization, and higher electrical breakdown field are the most promising candidates. According to this rule, so far, four kinds of materials, namely antiferroelectrics, dielectric glass-ceramics, relaxor ferroelectric and polymer-based ferroelectrics are thought to be more likely used in next-generation pulsed capacitors, and have been widely studied. Thus, this review serves to give an overall summary on the state-of-the-art progress on electric energy-storage performance in these materials. Moreover, some general future prospects are also provided from the existed theoretical and experimental results in this work, in order to propel their application in practice.