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High energy electron radiation effect on Ni/4H-SiC SBD and Ohmic contact

Zhang Lin,Zhang Yi-Men,Zhang Yu-Ming,Han Chao,Ma Yong-Ji,

中国物理 B , 2009,
Abstract: The Ni/4H-SiC Schottky barrier diodes (SBDs) and transfer length method (TLM) test patterns of Ni/4H-SiC Ohmic contacts were fabricated, and irradiated with 1~MeV electrons up to a dose of 3.43$\times 10^{14}$~e/cm$^{ - 2}$. After radiation, the forward currents of the SBDs at 2~V decreased by about 50{\%}, and the reverse currents at $-200$~V increased by less than 30{\%}. Schottky barrier height ($\phi _{\rm B} )$ of the Ni/4H-SiC SBD increased from 1.20~eV to 1.21~eV under 0~V irradiation bias, and decreased from 1.25~eV to 1.19~eV under $-30$~V irradiation bias. The degradation of $\phi _{\rm B} $ could be explained by the variation of interface states of Schottky contacts. The on-state resistance ($R_{\rm s}$) and the reverse current increased with the dose, which can be ascribed to the radiation defects in bulk material. The specific contact resistance ($\rho _{\rm c})$ of the Ni/SiC Ohmic contact increased from 5.11$\times 10^{ - 5}~{\Omega}\cdot$\,cm$^{2}$ to 2.97$\times $10$^{ - 4}~{\Omega}\cdot$\,cm$^{2}$.
Influence of Carbon Layer on the Properties of Ni-Based Ohmic Contact to n-Type 4H-SiC  [PDF]
A. Kuchuk,V. Kladko,Z. Adamus,M. Wzorek,M. Borysiewicz,P. Borowicz,A. Barcz,K. Golaszewska,A. Piotrowska
ISRN Electronics , 2013, DOI: 10.1155/2013/271658
Abstract: Nickel-based contacts with additional interfacial layer of carbon, deposited on n-type 4H-SiC, were annealed at temperatures ranging from 600 to 1000°C and the evolution of the electrical and structural properties were analyzed by I-V measurements, SIMS, TEM, and Raman spectroscopy. Ohmic contact is formed after annealing at 800°C and minimal specific contact resistance of about ???cm2 has been achieved after annealing at 1000°C. The interfacial carbon is amorphous in as-deposited state and rapidly diffuses and dissolves in nickel forming graphitized carbon. This process activates interfacial reaction between Ni and SiC at lower temperature than usual and causes the formation of ohmic contact at relatively low temperature. However, our results show that the specific contact resistance as well as interface quality of contacts was not improved, if additional layer of carbon is placed between Ni and SiC. 1. Introduction Owing to its excellent intrinsic properties such as high thermal conductivity, high electric field breakdown strength, and high saturation, electron silicon carbide (SiC) is well recognized as an attractive material for application in high-power devices operating in high-temperature environment [1]. Much effort has been undertaken to master the SiC growth, both in form of ingots and of the epitaxial thin films, and important progress has been made in these fields during last two decades. However, in order to fully exploit this potential it is still necessary to overcome several technical issues related to the semiconductor processing and fabrication of power electronic devices; development of reliable ohmic contacts is one of the key problems in this respect [2]. The fabrication of ohmic contacts to SiC may be achieved by using various metallization schemes; as for the n-type SiC, Ni, and Ni-based contacts are the most commonly used ones. They are formed by high temperature annealing at temperatures in the range 950–1050°C for time of 2–15 minutes [3–6]. Although many experimental works have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain Schottky to Ohmic transition, the final picture is still far from completeness. There is no doubt that Ni very easily react with SiC forming the whole spectrum of nickel silicides, depending on details of ohmic contact fabrication. On the other hand there is a strong evidence that fabrication of silicides, via contact reaction of Ni with SiC or via deposition of the specific silicide does not provide solely an ohmic contact with
Nanoscale electro-structural characterisation of ohmic contacts formed on p-type implanted 4H-SiC  [cached]
Frazzetto Alessia,Giannazzo Filippo,Lo Nigro Raffaella,Di Franco Salvatore
Nanoscale Research Letters , 2011,
Abstract: This work reports a nanoscale electro-structural characterisation of Ti/Al ohmic contacts formed on p-type Al-implanted silicon carbide (4H-SiC). The morphological and the electrical properties of the Al-implanted layer, annealed at 1700°C with or without a protective capping layer, and of the ohmic contacts were studied using atomic force microscopy [AFM], transmission line model measurements and local current measurements performed with conductive AFM. The characteristics of the contacts were significantly affected by the roughness of the underlying SiC. In particular, the surface roughness of the Al-implanted SiC regions annealed at 1700°C could be strongly reduced using a protective carbon capping layer during annealing. This latter resulted in an improved surface morphology and specific contact resistance of the Ti/Al ohmic contacts formed on these regions. The microstructure of the contacts was monitored by X-ray diffraction analysis and a cross-sectional transmission electron microscopy, and correlated with the electrical results.
Ti(20 nm)/Al(30 nm)/P型4H-SiC LDMOSFET欧姆接触的改善
The Improvement of Ohmic Contacts Property in P-Type 4H-SiC LDMOSFET Using Ti(20 nm)/Al(30 nm) Electrodes

裴紫微, 陈晨, 杨霏, 许恒宇, 张静, 万彩萍, 刘金彪, 李俊峰, 金智, 刘新宇
Smart Grid (SG) , 2015, DOI: 10.12677/SG.2015.56036
碳化硅横向双扩散金属-氧化物-半导体晶体管(Silicon Carbide laterally diffused Metal-Oxide-Semi- conductor Field Effect Transistor, SiC LDMOSFET)在高压集成电路中有着越来越广泛的应用前景。目前为止,依旧存在着限制SiC LDMOSFET器件进一步发展的瓶颈,欧姆接触便是其中之一。对于p型碳化硅,金属铝被认为是有利于形成欧姆接触的材料,但厚度较厚。研究表明,钛的加入能减小接触电阻,提高热稳定性。主要研究了一种新组分的钛/铝薄层金属用于p型4H-SiC的欧姆接触。通过溅射台将Ti(20 nm)/Al(30 nm)金属电极先后溅射到掺杂浓度为1 × 1020 cm?3的p型4H-SiC上,然后在氩气氛围中快速热退火(退火温度为1000℃,时间为2.5 min)形成欧姆接触。用传输线方法测量比接触电阻。最终得到比接触电阻值的优值为5.71 × 10?4 Ω?cm2,比预期结果的比接触电阻值降低了一个量级。此结果对Ti/Al基p型SiC LDMOSFET的进一步研究有着积极的意义。
Silicon Carbide laterally diffused Metal-Oxide-Semiconductor Field Effect Transistor (SiC LDMOSFET) is widely used in high voltage integrated circuits. Until now, one of the obstacles which restrict its further development is its ohmic contact with p-type SiC. Previously, Aluminum is used to form the ohmic contact for p-type SiC. To form the ohmic contact with p-type SiC, Al metal was deposited and then annealed at high temperature subsequently. However, at high temperature, its thermal stability is supposed to be degraded, and will make the device performance getting worse. The re-search showed that the addition of titanium can decrease the contact resistance and improve the thermal stability. In this paper, a Ti(20 nm)/Al(30 nm) contact was formed by sputtering on p-type 4H-SiC Epitaxial film respectively with doping concentration of 1 × 1020 cm?3. Then, rapid thermal annealing was performed in argon atmosphere at 1000?C for 2 min to form the ohmic contact. Transmission-line-model (TLM) method was examined to extract the contact resistivity. In case of Ti(20 nm)/Al(30 nm)/p-type SiC, a specific contact resistance of 5.71 × 10?4 Ω?cm2 was obtained, nearly one order of magnitude lower than the respected value. This research has a positive effect on the device performance of SiC LDMOSFETs.
Ohmic Heating Suspends, not Reverses, the Cooling Contraction of Hot Jupiters  [PDF]
Yanqin Wu,Yoram Lithwick
Physics , 2012, DOI: 10.1088/0004-637X/763/1/13
Abstract: We study the radius evolution of close-in extra-solar jupiters under Ohmic heating, a mechanism that was recently proposed to explain the large observed sizes of many of these planets. Planets are born with high entropy and they subsequently cool and contract. We focus on two cases: first, that ohmic heating commences when the planet is hot (high entropy); and second, that it commences after the planet has cooled. In the former case, we use analytical scalings and numerical experiments to confirm that Ohmic heating is capable of suspending the cooling as long as a few percent of the stellar irradiation is converted into Ohmic heating, and the planet has a surface wind that extends to pressures of ~10 bar or deeper. For these parameters, the radii at which cooling is stalled are consistent with (or larger than) the observed radii of most planets. The only two exceptions are WASP-17b and HAT-P-32b. In contrast to the high entropy case, we show that Ohmic heating cannot significantly re-inflate planets after they have already cooled. This leads us to suggest that the diversity of radii observed in hot jupiters may be partially explained by the different epochs at which they are migrated to their current locations.
Ohmic Heating for Tofu Making—A Pilot Study  [PDF]
Cheng-Chang Lien, Yu-Chieh Shen, Ching-Hua Ting
Journal of Agricultural Chemistry and Environment (JACEN) , 2014, DOI: 10.4236/jacen.2014.32B002

The aim of this study is to explore the relationship between temperature and electrical conductivity of soya milk under ohmic heating in tofu making. The soya milk of 10 Brix was heated to a steady temperature of 90?C. The applied voltage was increased and the temperature rising rate was investigated for adequate heating profiles in tofu making. Experimental results showed that the electrical conductivity of soya milk is proportional to the heating time. The temperature rising rate was increased from 1.46?C to 3.82?C/min as a result of increased voltage. Hence ohmic heating could be an efficient, convenient heating measure in tofu making.

Characterising the Progress of Gelation in Tofu Making with Ohmic Heating  [PDF]
Cheng-Chang Lien, Ching-Hua Ting
Journal of Agricultural Chemistry and Environment (JACEN) , 2015, DOI: 10.4236/jacen.2015.42B001

In tofu making by heat treatment, the addition of coagulant ionizes the proteins as a result of heat dissolution and the ionized proteins aggregate with the coagulant to form protein clusters. The electrical conductivity (EC) of the soya milk emulsion varies in response to the progress of gelation. By ohmic heating, the applied current and voltage directly indicate the electrical conductivity of the soya milk emulsion and then indirectly the progress of tofu gelation. In this paper, ultrasonic measurement is adopted to explore the feasibility of using EC as an indicator of tofu gelation. Experiments showed a strong correlation between EC and ultrasonic measurement in characterisation of tofu gelation.

Fabrication and characteristics of a 4H-SiC junction barrier Schottky diode

半导体学报 , 2011,
Abstract: 4H-SiC junction barrier Schottky (JBS) diodes with four kinds of design have been fabricated and characterized using two different processes in which one is fabricated by making the P-type ohmic contact of the anode independently, and the other is processed by depositing a Schottky metal multi-layer on the whole anode. The reverse performances are compared to find the influences of these factors. The results show that JBS diodes with field guard rings have a lower reverse current density and a higher breakdown voltage, and with independent P-type ohmic contact manufacturing, the reverse performance of 4H-SiC JBS diodes can be improved effectively. Furthermore, the P-type ohmic contact is studied in this work.
Ohmic contacts of 4H-SiC on ion-implantation layers

Wang Shou-Guo,Zhang Yan,Zhang Yi-Men,Zhang Yu-Ming,

中国物理 B , 2010,
Abstract: Ion-implantation layers are fabricated by multiple nitrogen ion-implantations (3 times for sample A and 4 times for sample B) into a p-type 4H-SiC epitaxial layer. The implantation depth profiles are calculated by using the Monte Carlo simulator TRIM. The fabrication process and the $I$--$V$ and $C$--$V$ characteristics of the lateral Ti/4H-SiC Schottky barrier diodes (SBDs) fabricated on these multiple box-like ion-implantation layers are presented in detail. Measurements of the reverse $I$--$V$ characteristics demonstrate a low reverse current, which is good enough for many SiC-based devices such as SiC metal--semiconductor field-effect transistors (MESFETs), and SiC static induction transistors (SITs). The parameters of the diodes are extracted from the forward $I$--$V$ and $C$--$V$ characteristics. The values of ideality factor $n$ of SBDs for samples A and B are 3.0 and 3.5 respectively, and the values of series resistance $R_{\rm s} $ are 11.9 and 1.0~k$\Omega $ respectively. The values of barrier height $\phi _{\rm B} $ of Ti/4H-SiC are 0.95 and 0.72 eV obtained by the $I$--$V$ method and 1.14 and 0.93 eV obtained by the $C$--$V$ method for samples A and B respectively. The activation rates for the implanted nitrogen ions of samples A and B are 2{\%} and 4{\%} respectively extracted from $C$--$V$ testing results.
Influence of Ohmic Heating on Advection-Dominated Accretion Flows  [PDF]
G. S. Bisnovatyi-Kogan,R. V. E. Lovelace
Physics , 1997, DOI: 10.1086/310826
Abstract: Advection-dominated, high-temperature, quasi-spherical accretion flow onto a compact object, recently considered by a number of authors, assume that the dissipation of turbulent energy of the flow heats the ions and that the dissipated energy is advected inward. It is suggested that the efficiency of conversion of accretion energy to radiation can be very much smaller than unity. However, it is likely that the flows have an equipartition magnetic field with the result that dissipation of magnetic energy at a rate comparable to that for the turbulence must occur by Ohmic heating. We argue that this heating occurs as a result of plasma instabilities and that the relevant instabilities are current driven in response to the strong electric fields parallel to the magnetic field. We argue further that these instabilities heat predominantly the electrons. We conclude that the efficiency of conversion of accretion energy to radiation can be much smaller than unity only for the unlikely condition that the Ohmic heating of the electrons is negligible.
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