Browsing by Author "Wu, Tian-Li"

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Analysis of the Gate Capacitance-Voltage Characteristics in p-GaN/AlGaN/GaN Heterostructures
(2017-12-01)
Wu, Tian-Li
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Bakeroot, Benoit
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Liang, Hu
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Posthuma, Niels
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You, Shuzhen
In this letter, we analyzed the gate capacitance characteristics in p-GaN gate/AlGaN/GaN heterostructures by using a two-junction capacitor model. First, we have observed that the C-V behavior depends on the different processing conditions of the p-GaN gate. Second, a two-junction capacitor model considering a series connection of the Schottky metal/p-GaN junction capacitor and the AlGaN barrier capacitor is proposed to explain this C-V behavior. Based on this model, the junction capacitance has an influence on the total capacitance value under a high gate bias due to the Schottky metal/p-GaN junction. Furthermore, the Mg-concentration and hole density can be extracted. The extracted hole density is consistent with the results obtained by Hall measurements.
Bias- and Temperature-Assisted Trapping/De-trapping of R-ON Degradation in D-mode AlGaN/GaN MIS-HEMTs on a Si substrate
(2017-01-01)
Zhang, Jin-Ming
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Hsieh, Ting-En
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Wu, Tian-Li
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Chen, Szu-Hao
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Chen, Shi-Xuan
In this study, we investigate the R-ON degradation in D-mode AlGaN/GaN MIS-HEMTs on a Si substrate via an accelerated step stress at different temperatures. We have observed a three-phase R-ON degradation behavior, which is highly correlated with a drain bias and back gate bias. First, the R-ON degradation increases till a peak value when the drain bias increases. Second, when the drain bias increases further, the R-ON degradation is reduced. Third, the R-ON degradation slowly increases again. R-ON degradation is characterized with different temperatures, the results show that 1) high temperature leads to a smaller R-ON degradation compared to the result at room temperature and 2) high temperature shifts the peak of the R-ON degradation at a lower drain bias. A possible mechanism that the trapping and de-trapping could occur due to the high temperature and high drain bias is proposed to explain the observed results.
Characteristics of 4H-SiC RF MOSFETs on a Semi-insulating Substrate
(2011)
Wu, Tian-Li
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Huang, Chih-Fang
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Cheng, Chun-Hu
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
This study has provided considerable insight into the impact of device down scaling on the characteristics of RF devices. This type of RF devices, featuring a thin p-layer based on a semi-insulating substrate, is free from the unwanted parasitic effects resulting from traditional conducting substrates. We fabricated 4H-SiC RF MOSFETs with f(T)/f(MAX) of 0.7/1.5 GHz and, in so doing, identified the key issues associated with short channel effects, influencing device mobility and the RF characteristics of RF MOSFETs on a semi-insulating substrate.
Demonstration of Annealing-free Metal-Insulator-Semiconductor (MIS) Ohmic Contacts on a GaN Substrate using Low Work-function Metal Ytterbium (Yb) and Al2O3 Interfacial Layer
(2019-01-01)
Wu, Tian-Li
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Tseng, Yang-Yan
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Huang, Chih-Fang
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Chen, Zih-Sin
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Lin, Chih-Chien
In this letter, the Metal-Insulator-Semiconductor (MIS) contacts are fabricated on the GaN substrates and compared to the Metal-Semiconductor (MS) contacts. To alleviate the Fermi level pinning effect at the Metal-Semiconductor interface, an Al2O3 interfacial layer (IL) (1 similar to 3 nm) is used to form the MIS contacts. By comparing the electrical characteristics, the contact with Onm Al2O3 layer, i.e., MS contact, shows a lowest current compared to the contacts with an Al2O3 IL, i.e., MIS contact. Furthermore, the current at 0.5V in the fabricated Transmission Line Measurement (TLM) device with lnm Al2O3 IL is 10(3) times higher the one without an Al2O3 IL. This proves that inserting an Al2O3 IL could mitigate the Fermi level pinning, resulting in a low Schottky barrier height. Finally, based on the TLM analysis, the resistivity of 5.1x10(-4) Omega.cm(2) is demonstrated in the MIS contact with lnm Al2O3 IL.
Design and analysis of high electron mobility transistor inspired: III-V electro-optic modulator topologies
(2020-09-01)
Das, Pallabi
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Wu, Tian-Li
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Tallur, Siddharth
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交大名義發表
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National Chiao Tung University
III-V heterostructure based high electron mobility transistors (HEMTs) offer superior performance as compared to CMOS silicon transistors owing to the high mobility in the 2D electron gas (2DEG) channel at the heterostructure interface. Gallium nitride (GaN) based HEMTs are also suitable for high power and high temperature applications. GaN has a rich offering of material properties spanning domains of non-linear optics, piezoelectric micro-electro-mechanical systems, and monolithic microwave integrated circuits. In this paper, we propose HEMT inspired III-V electro-optic modulator topologies and study the light interaction with 2DEG in such structures. We analyze the electroabsorption and electrorefraction on account of the 2DEG interaction with light and present a design framework to selectively leverage the desired mechanism of modulation. Our analysis suggests that modulation index of electrorefractive modulation in a HEMT-like structure is comparable to silicon photonic modulators. By leveraging the higher electron mobility in these material platforms, the device concepts proposed here could potentially be used to design electro-optic modulators with extremely high modulation rates.
Effects of Annealing on Ferroelectric Hafnium-Zirconium-Oxide-Based Transistor Technology
(2019-03-01)
Chen, Yi-Hsuan
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Su, Chun-Jung
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Hu, Chenming
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Wu, Tian-Li
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國際半導體學院
In this letter, we investigate annealing effects in ferroelectric HfZrOx dielectric in metal-insulator-metal devices and metal-oxide-semiconductor capacitors by comparing two annealing methods: rapid thermal annealing (RTA) and microwave annealing (MWA). The tradeoff characteristics between the annealing conditions, polarization-electric field characteristics, gate leakage current, and interface state density (D-it) are discussed. We show that: 1) a positive correlation between the remanent polarization (Pr), the gate leakage current, and D-it as the annealing temperature (RTA) and the annealing power (MWA) increase and 2) the MWA is promising for ferroelectric transistors technology, since its low thermal budget can minimize D-it and avoid increase in the gate leakage current.
Effects of gamma-Ray Irradiation on AlGaN/GaN Heterostructures and High Electron Mobility Transistor Devices
(1970-01-01)
Sharma, Chandan
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Singh, Rajendra
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Chao, Der-Sheng
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Wu, Tian-Li
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國際半導體學院
This study examined the effects of three cumulative c-ray irradiation doses on AlGaN/GaN epilayer material and on high electron mobility transistor (HEMT) devices. After a cumulative gamma-ray dose of 16 kGy, the Hall mobility increased from 1800 cm(2)/V s to 2100 cm(2)/V s, as determined through Hall measurement. Atomic force microscopy indicated an improvement in surface roughness but no change in the surface potential (theta(s)). The HEMT device exhibited improvement in the drain current, with a subtle decreasing tendency in the leakage current. At high doses of gamma-ray irradiation, the trends in the material and device parameters saturated. Moreover, the metal-semiconductor interface degraded, as confirmed through scanning electron microscopy image analysis.
Gamma-Ray Irradiation Effect on Ferroelectric Devices with Hafnium Aluminum Oxides
(2019-12-01)
Liu, Chien
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Tung, Yi-Chun
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Wu, Tian-Li
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Cheng, Chun-Hu
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Tseng, Chih-Yang
Herein, the gamma-ray irradiation effect on ferroelectric HfAlO(x)capacitors for biomedical and space applications is investigated. The experimental results focus on the observation of ferroelectric polarization characteristics in support of different defect mechanisms induced by annealing, endurance cycling, and gamma-ray irradiation. It is found that the HfAlO(x)with low Al doping of 6.5% become more vulnerable to radiation exposure, but a remarkable improvement in 9%-Al-doped HfAlO(x)due to less oxygen vacancies is demonstrated. In addition, the results also confirm that the fatigue property of ferroelectric HfAlO(x)capacitor is determined by the electric-stress-induced defect during endurance cycling, not mainly contributed by irradiation damage, which shows the potential for memory applications in rigorous irradiation environment.
Impact of the polarization on time-dependent dielectric breakdown in ferroelectric Hf0.5Zr0.5O2 on Ge substrates
(2020-04-01)
Yang, Ting-Hsin
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Su, Chun-Jung
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Wang, Yu-Shun
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Kao, Kuo-Hsing
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Lee, Yao-Jen
In this work, polarization-dependent time-dependent dielectric breakdown in ferroelectric HZO Ge MOSCAPs presented. First, ferroelectric HZO Ge MOSCAPs with and without in-situ NH3 plasma interfacial layer, treatment exhibit the two distinct remnant polarization (P-r), Secondly the device with a larger P-r shows a higher gate leakage current and smaller time-to-breakdown (t(BD)) compared to the device with a smaller P-r. Then, a physical model based on the high probability of the electron tunneling accelerating the formation of the percolation path is proposed. Finally, the device with large P-r shows a lower extrapolated operating voltage. However more than 1.5 V of the extracted operation voltage for 1% failure of 10 year lifetime in the device with large P-r still can be obtained. (C) 2020 The Japan Society of Applied Physics
Improved TDDB Reliability and Interface States in 5-nm Hf0.5Zr0.5O2 Ferroelectric Technologies Using NH3 Plasma and Microwave Annealing
(2020-04-01)
Chen, Yi-Hsuan
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Su, Chun-Jung
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Yang, Ting-Hsin
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Hu, Chenming
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Wu, Tian-Li
This article reports that the enhanced forward gate bias time-dependent dielectric breakdown (TDDB) reliability and interface quality are achieved in 5-nm ferroelectric Hf0.5Zr0.5O2 (HZO) technologies by using the NH3 plasma interfacial layer (IL) treatment and microwave annealing (MWA). An orthorhombic crystalline phase is observed in the annealed HZO film with NH3 plasma IL treatment and MWA, and NH3 plasma IL treatment can suppress Hf/Zr interdiffusion. Metal-oxide-semiconductor capacitors (MOSCAPs) subjected to NH3 plasma IL treatment and 2100-W MWA also have a higher extrapolated operating voltage for a ten-year lifetime at 0.01% failure and lower interface state density compared to the devices subjected to only rapid thermal annealing (RTA) at 600 degrees C. Therefore, NH3 plasma treatment and MWA are effective for improving the TDDB reliability and interface quality of the ultrathin ferroelectric HZO.
Investigation of Degradation Phenomena in GaN-on-Si Power MIS-HEMTs under Source Current and Drain Bias Stresses
(2018-01-01)
Yang, Chih-Yi
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Wu, Tian-Li
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Hsieh, Tin-En
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Chang, Edward Yi
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材料科學與工程學系
In this paper, we investigate the degradation phenomena in GaN-on-Si Metal-Insulator-Semiconductor High electron Mobility Transistors (MIS-HEMTs) in the cascode topography for enhancement mode power switching applications. Different stress conditions, e.g., constant source current (Is=100(mu A)=2(mA/mm) and 100(nA)=2 x 10(-3)(mA/mm)) and drain voltages (V-D=1(V), 10(V), 100(V), and 200(V)), are used to investigate the source current and drain bias dependent degradation. First, the VTH shift is correlated with the RoN increase under a low drain bias stress (V-D<10(V)). However, under a high drain bias stress, the trapping location is most probably in the gate-to-drain access region, leading a different degradation phenomena compared to the case under a low drain bias stress. Furthermore, we found that the devices are stressed under a different source current stress show a similar degradation phenomenon. This suggests that, in the cascode circuit topology, the instability degradation is still mainly triggered by the drain bias.
Investigation of Recessed Gate AlGaN/GaN MIS-HEMTs with Double AlGaN Barrier Designs toward an Enhancement-Mode Characteristic
(2020-02-01)
Wu, Tian-Li
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Tang, Shun-Wei
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Jiang, Hong-Jia
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國際半導體學院
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International College of Semiconductor Technology
In this work, recessed gate AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with double AlGaN barrier designs are fabricated and investigated. Two different recessed depths are designed, leading to a 5 nm and a 3 nm remaining bottom AlGaN barrier under the gate region, and two different Al% (15% and 20%) in the bottom AlGaN barriers are designed. First of all, a double hump trans-conductance (g(m))-gate voltage (V-G) characteristic is observed in a recessed gate AlGaN/GaN MIS-HEMT with a 5 nm remaining bottom Al0.2Ga0.8N barrier under the gate region. Secondly, a physical model is proposed to explain this double channel characteristic by means of a formation of a top channel below the gate dielectric under a positive V-G. Finally, the impacts of Al% content (15% and 20%) in the bottom AlGaN barrier and 5 nm/3 nm remaining bottom AlGaN barriers under the gate region are studied in detail, indicating that lowering Al% content in the bottom can increase the threshold voltage (V-TH) toward an enhancement-mode characteristic.
Investigation of the degradations in power GaN-on-Si MIS-HEMTs subjected to cumulative gamma-ray irradiation
(2019-09-01)
Sharma, Chandan
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Modolo, Nicola
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Chen, Hsi-Han
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Tseng, Yang-Yan
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Tang, Shun-Wei
In this work, GaN-on-Si power Metal-Insulator-Semiconductor High Electron Mobility Transistors(MIS-HEMTs) are irradiated through different regimes of cumulative gamma-ray irradiation, namely 1, 2, 3, 4, and 5 kGy for the first sample; 1, 3, and 5 kGy for the second sample; 1, 5, and 10 kGy for the third sample; and 1, 10, and 20 kGy for the fourth sample. After each irradiation dose, drain current (ID), threshold voltage (I-g), and gate leakage current (Is) are electrically characterized in all the samples. An improvement in I-D with a shift in V-Th is observed in all the samples, which saturates after a higher irradiation dose. X-ray photoelectron spectroscopy (XPS) analysis confirms creation of nitrogen vacancies that act as donor and improves the I-D. No significant change in I-g is observed except for an increase in noise in gate leakage current. Scanning electron microscopy (SEM) shows the Al-based metallization pad degrades due to formation of small cavities. Finally, energy dispersive X-ray (EDX) analysis confirms the formation of Al native oxides due to gamma-ray irradiation.
Numerical Study of 4H-SiC UMOSFETs with Split-Gate and P plus Shielding
(2020-03-01)
Jiang, Jheng-Yi
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Wu, Tian-Li
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Zhao, Feng
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Huang, Chih-Fang
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國際半導體學院
In this paper, performances of a 4H-SiC UMOSFET with split gate and P+ shielding in different configurations are simulated and compared, with an emphasis on the switching characteristics and short circuit capability. A novel structure with the split gate in touch with the P+ shielding is proposed. The key design issues for 4H-SiC UMOSFETs are trench gate dielectric protection and reverse transfer capacitance Crss reduction. Based on simulation results, it is concluded that a UMOSFET with a gate structure combining split gate grounded to the trench bottom protection P+ shielding layer and a current spreading layer is achieved to yield the best compromise between conduction, switching, and short circuit performance. The split-gate design can effectively reduce Crss by shielding the coupling between the gate electrode and the drain region. The P+ shielding design not only protects the oxide at trench bottom corners but also minimizes the short channel effect due to drain-induced barrier lowing and the channel length modulation. Trade-off of the doping concentration of current spreading layer for UMOSFET is also discussed. A heavily doped current spreading layer may increase Crss and influence the switching time, even though R-ON,R-SP is reduced.
Study on the effects of Si implantation on the interface of 4H-SiC lateral MOSFETs
(2020-04-01)
Jiang, Jheng-Yi
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Hung, Jia-Qing
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Huang, Pin-Wei
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Wu, Tian-Li
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Huang, Chi-Fang
In this study, Si implantation was used to improve the interface properties of SiC/SiO2 in 4H-SiC lateral MOSFETs. In lateral n-channel MOSFETs, a 4%-6% improvement on the linear and saturation current was observed with Si implantation, From high/low-frequency CV measurements, the Si implanted n-type MOS capacitor showed a 20% lower interface state density than the non-implanted ones at an energy level of E-C - E = 0.2 eV, without degrading oxide integrity. Lateral p-channel MOSFETs, on the other hand, showed a 36.5% reduction in the linear current and a 16.6% reduction in the saturation current with Si implantation. Furthermore, the temperature coefficients of lateral and vertical MOSFETs implanted, by Si ere monitored up to 175 degrees C. The temperature coefficients of the Si-implanted n-channel and p-channel lateral MOSFETs were nearly identical to those of their non-implanted counterparts. (C) 2020 The Japan Society of Applied Physics
Understanding gamma-Ray Induced Instability in AlGaN/GaN HEMTs Using a Physics-Based Compact Model
(2020-03-01)
Sharma, Chandan
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Modolo, Nicola
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Wu, Tian-Li
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Meneghini, Matteo
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Meneghesso, Gaudenzio
In this article, we demonstrate that a physics-based compactmodel can facilitate to analyze the reliability using an example of gamma-ray induced instability in AlGaN/GaN HEMTs. First, the typical AlGaN/GaN HEMTs are subjected to the cumulative gamma-ray irradiation, exhibiting the drain current (I-D) increase. In order to further elucidation, the root cause, the compact model is implemented and calibrated with the pristine case. Then, I-D-V-G and I-D-V-D characteristics subjected to the gamma-ray irradiation are fitted with the compact model. The extracted mu and R-c are consistent with the results obtained by the Hall measurement and circular transmission line measurement (C-TLM). By comparing the fitted curves with considering: 1) fitted mu (R-c is fixed as the pristine case) and 2) fitted R-c (mu is fixed as the pristine case), the shift of mu is identified as the root cause leading to the I-D increase because of the better fitting results. Therefore, with the assistance of the physics-based compact model, the shift of the parameter can be further analyzed to understand the origin of the instability.