ICMCTF2016 Session C5-2: Thin Films for Active Devices

Monday, April 25, 2016 1:30 PM in Room Sunset

Monday Afternoon

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1:30 PM C5-2-1 Atomic Layer Deposition of GaN using GaCl3 and N2 on Si Wafers
Birol Kuyel, Hugo Redondo, Alex Alphonse (Nano-Master, Inc., USA)

Depositing nitrates using N2 rather than NH3 requires plasma activation. It has been done successfully for Si3N4 in a PECVD system and for GaN in an MOCVD system. As a result better films without H2 content depositied at lower temperatures and without the abatment issues relating to NH3 use. However carrying the earlier learning to atomic deposition systems without sacrificing productivity or cycle time is none trivial. Nano-Master has developed an ALD chamber with ICP source having a minimal volume and therefore shortest cycle time. Here the features of the chamber design and results of depositing GaN films on Si substrates in such a system will be discussed.

1:50 PM C5-2-2 AlN Buffer Layers for a Selective Growth of GaN by MOCVD on Patterned Sapphire
Dominik Jaeger (Evatec, Switzerland); Jan Wagner, Michael Jetter (IHFG, Germany); Hartmut Rohrmann (Evatec, Switzerland)

For the production of high brightness light-emitting diodes (LEDs) it is essential to have both a high light extraction efficiency (LEE) and high internal quantum efficiency (IQE) of the device. Patterned sapphire substrates (PSS) improve both the LEE and the IQE and hence PSS are often used for high brightness LEDs. The LED itself is built of multi quantum well (MQW) structures containing metalorganic vapor phase epitaxy (MOVPE)-GaN layers. Any defect in these layers results in a decrease of the IQE.

In this work an AlN-buffer layer, using physical vapor deposited (PVD), is used as a template for the MOVPE-GaN growth. All AlN films were deposited on a dedicated high temperature PVD module using an Evatec CLUSTERLINE 200 II. Commercially available patterned and flat sapphire substrates (FSS) were processed simultaneously. Both the deposition temperature and thickness were varied from 400°C to 800°C and from 10 nm to 65 nm respectively.

The following MOVPE processes were performed in an Aixtron 200RF with a horizontal reactor and standard precursors for the GaN deposition. After a low temperature GaN nucleation step at 750°C, the temperature is raised up to 1120°C for the GaN film growth. The thicknesses were varied between approx. 20 nm and 3 µm.

XRD measurements show that the AlN on FSS are of high quality and their FWHM of the AlN(002) rocking curve (RC) is below 20 arcsec. Scanning electron microscope (SEM) images show that the growth pattern of GaN on PSS does not only depend on the RC, but also on the lattice spacing of AlN, which can be slightly varied by temperature and thickness. Depending on this lattice spacing, the GaN-MOVPE layer either shows a side wall or a bottom growth. A process window for the AlN-PVD buffer layer is presented in which the GaN grows only at the bottom of PSS. Hence these AlN templates are suitable for the mass production of high brightness LEDs.

2:10 PM C5-2-3 Ytterbium β-diketonate Complexes for Near Infra-Red Organic Light-Emitting Devices
Zubair Ahmed, Rian Aderne, Jiang Kai, Marco Cremona (PUC-Rio, Brazil)

The near-infrared (NIR) emitting lanthanide complexes are gaining much attention all over the world for their potential applications in optical communications, optoelectronic devices and biomedical diagnostic applications. In particular, ytterbium ion is very useful for biomedical probes because it emits light near 1000 nm where the tissues are relatively transparent. The emission at this wavelength can be properly utilized to develop OLEDs using Yb complexes as emitting layers. Although few OLEDs based Yb complexes are available, their efficiency and stability are very low and, is still in question. For this reason, there is a need to develop ytterbium complexes which could enhanced the efficiency and stability of the respective OLEDs.

In this work, Yb complexes based on various fluorinated/non-fluorinated β-diketones and ancillary N-/O-donor neutral ligands were synthesized and fully characterized. The photophysical studies (quantum efficiency and time resolve spectroscopy) of solution and thin film of the complexes were done to select the best complexes for the fabrication of stable and efficient OLEDs. Finally, the OLEDs were fabricated and investigated using these complexes as emitting layers along with other organic layers like NPB (hole-transporting layer), BCP (hole-blocker) and Alq3 (electron-transporting layer). The layers were sequentially deposited under high vacuum environment by thermal evaporation onto ITO glass substrates. Additionally, co-deposition technique with a specific organic matrix (TcTa) was used to improve charge transport in the devices and to avoid quenching phenomena. In this case, the typical device structure was: ITO/NPB(25nm)/TcTa:Yb-complex (40 nm)/BCP (20nm)/Alq3(20nm)/LiF/Al where the Yb complex was used as dopant with a 10% wt. concentration. The fabricated devices showed strong emission at 1035 nm correspondent to the 2F5/22F7/2 transition,a characteristic of Yb3+ ion together with a visible broad emission mainly coming from Alq3 and organic matrix. All the devices showed good efficiency as well as electrical stability with a threshold voltage of about 6 V. The results and the potential applications for NIR-OLEDs will be presented and discussed.
2:30 PM C5-2-4 The Impact of TiN Gate Thickness on Performance and Negative Bias Temperature Instability in p- MOSFET with HfxZr1-xO2 High-k Layer
Kuan-Ju Liu, Ting-Chang Chang, Chien-Yu Lin (National Sun Yat-Sen University, Taiwan, Republic of China)
In this research, the effects of metal gate thickness on negative bias temperature instability (NBTI) degradation in TiN/HfxZr1-xO2 p-channel metal-oxide-semiconductor field effect transistors are studied. The input/output devices (equivalent oxide thickness of 39Å) with thinner TiN gate show higher mobility and less NBTI degradation. This indicates that N species can diffuse to the Si/SiO2 interface and become the main mobility and NBTI reliability killer. However, NBTI degradation indicates that standard performance devices (equivalent oxide thickness of 17Å), which hole-trapping can easily take place in high-k bulk, with a thicker TiN layer has more high-k bulk traps, and therefore nitrogen diffusion from TiN is not adequate to explain all the phenomena. The more high-k bulk traps can be attributed to more abundant oxygen vacancies due to stronger driving force of oxygen diffusion from HfxZr1-xO2 layer toward TiN gate. Furthermore, the obtained results of charge pumping measurement verify the proposed model.
2:50 PM C5-2-5 Transition-metal Nitrides as Semiconductors: ScN, CrN, and Related Alloys
Daniel Gall (Rensselaer Polytechnic Institute, USA)

ScN, CrN, and related ternary nitrides are semiconductors with promising properties for high-temperature electronic, thermoelectric, opto-electric, piezo-electric, and magnetoresistive devices. Epitaxial layers are grown on MgO(001) and Al2O3(0001) by reactive magnetron sputtering at 600-1000 oC, and their microstructure, surface morphology, and composition analyzed by XRD, XRR, in situ STM, RBS, XPS, and AES. A combination of temperature dependent electron transport measurements, optical analyses, and first principles calculations are employed to determine band gaps, effective masses, mobilities, carrier concentrations, and phonon modes. ScN has a 0.92 eV indirect band gap, direct transitions at the X and Gamma points of 2.07 and 3.75 eV, transport and effective masses of 0.40 and 0.33 m0, and a carrier concentration which is controlled by F doping ranging from 1.12-12.8x1020 cm-3. Al1-xScxN exhibits a structural instability with a non-linear composition dependence in bond angle, length, and character that is associated with a transition from the rock-salt to the wurtzite structure, and exhibits a direct band gap of 6.15–9.32x (eV) in the wurtzite structure. CrN is a Mott-Hubbard type insulator with a 0.2+/-0.4 eV band gap, a structural and magnetic phase transition at 280 K, variable-range hopping conduction with a Efros-Shklovskii to Mott transition at 30 K, a lower limit for the effective mass of 4.9 m0, and a donor ionization energy of 24 meV.

3:30 PM C5-2-7 Quasi-Ballistic Effect Influence Hot Carrier Degradation in Nanoscale n-MOSFET
Hsi-Wen Liu, Ting-Chang Chang, Jyun-Yu Tsai, Chien-Yu Lin, Ying-Hsin Lu, Ching-En Chen (National Sun Yat-Sen University, Taiwan, Republic of China)

In this research, Quasi-ballistic effect influence Hot carrier-induced degradation (HCD) at different temperature in ultra scale n-channel metal oxide semiconductor field effect transistor (n-MOSFET) was investigated. Since electron-electron scattering (EES) is the dominant mechanism in nanoscale device, which populates the hot carrier fraction more efficiently at elevated temperatures, making HCD more severe. Nevertheless, ballistic effect must be concerned in nanoscale device, but the ballistic effect influence on HCD is still not completely known. In this study, we use a concept of ballistic transport to explain why HCD can be suppressed under low temperature in short channel device. At low temperature, the injection velocity decreases and ballistic is enhanced because the population of the energetic carriers is decreased and scattering probability (ex. EES) is decreased in the channel, respectively.

3:50 PM C5-2-8 The Investigation on Defect Variation from Nitrogen Diffuse to Hafnium Oxide Layer in Metal-Oxide-Semiconductor Field Effect Transistors by Varying Metal Gate Fabrication
Ying-Hsin Lu, Ting-Chang Chang, Kuan-Ju Liu, Hsi-Wen Liu, Chien-Yu Lin (National Sun Yat-Sen University, Taiwan, Republic of China)

This study investigates on defect variation from Nitrogen diffuse to hafnium oxide layer in Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) by different metal gate fabrications. By varying fabrications of PVD-TiN, ALD-TiN and ALD-TaN, the work-function can be adjusted leading to apparent differences of threshold voltage (Vth). In addition, the result of the charge pumping shows that the amount of the interface trap in the PVD-TiN device is the highest, ALD-TiN device the second, while the ALD-TaN the least. On the other hand, nitrogen interstitial phenomenon resulting in temporary shift of threshold voltage (Vth) can be observed, PVD-TiN the highest and ALD-TaN the least, through ultra-fast and slow-IV NBTI. To compare with pre- and post-metal annealing effect on ALD-TaN, pre-metal annealing can suppress nitrogen interstitial from thermal diffusion in annealing process.

4:10 PM C5-2-9 Influence of Electrode Thermal Conductivity on Resistive Switching Behavior during Reset Process
Tian-Jian Chu, Tsung-Ming Tsai, Ting-Chang Chang, Kuan-Chang Chang (National Sun Yat-Sen University, Taiwan, Republic of China)
This study examines the influence of different electrode thermal conductivity on switching behavior during the reset process. Electrical analysis methods and an analysis of current conduction mechanism indicate that better thermal conductivity in the electrode will require larger input power in order to induce more active oxygen ions to take part in the reset process. More active oxygen ions cause a more complete reaction during the reset process, and cause the effective switching gap (dsw) to become thicker. The effect of the electrode thermal conductivity and input power are explained by our model and clarified by electrical analysis methods.
4:30 PM C5-2-10 Combined Effects of Light Illumination and Negative Gate-Bias on the Instability of a-InGaZnO Thin-Film Transistors
Chungyi Yang (National Chiao Tung University, Taiwan, Republic of China); Ting-Chang Chang (National Sun Yat-Sen University, Taiwan, Republic of China)
This letter investigates the combined effects of gate-bias and visible or ultraviolet light on the instability in InGaZnO thin-film transistors. Under the exposure to visible light, device exhibits stable characteristic without degradation, whereas UV light causes apparent subthreshold leakage and threshold voltage shift. On the other hand, negative gate-bias illumination stress under both visible and UV light leads to a pronounced threshold voltage shift. The effect of visible light on the instability of device can be manifested only when negative gate-bias is applied, and the cause can be speculated to be the thermionic-field emission process of hole-generation via trap-assisted photo-excitation.
4:50 PM C5-2-11 The Impact of Post-Metal Deposition Annealing Temperature on Performance and Reliability of High-k/Metal-Gate n-FinFETs
Chien-Yu Lin, Ting-Chang Chang, Kuan-Ju Liu, Xi-Wen Liu, Li-Hui Chen (National Sun Yat-Sen University, Taiwan, Republic of China)

In this research, the effects of post-metal deposition annealing temperature on the degradation induced by hot carrier stress (HCS) and positive bias stress (PBS) in TiN/HfO2 n-channel fin field effect transistors (FinFETs) are studied. The initial electrical characteristics possess higher threshold voltage (Vth), transconductance (GM) and on-state current (Ion) in high-annealing temperature devices. Particularly, it is found that the PBS and HCS-induced degradation is more serious in high-annealing temperature devices due to more plenty high-k bulk traps. However, nitrogen diffusion from TiN is not more abundant oxygen vacancies generated within HfO2 since oxygens are more likely to diffuse toward the interface layer and repair Si/SiO2 dangling bonds for high-annealing temperature devices. Furthermore, by charge-pumping and C-V measurements, less Nit and thicker IL was found in high-annealing temperature devices, verifying the proposed model.

5:10 PM C5-2-12 Investigating Characteristics and Reliability of a Dual Gate a-InGaZnO Thin Film Transistor with Etch Top Layer
Po-Yung Liao, Ting-Chang Chang, Tien-Yu Hsieh, Ming-Yen Tsai, Bo-Wei Chen, Ann-Kuo Chu (National Sun Yat-Sen University, Taiwan, Republic of China); Hua-Mao Chen (National Chiao Tung University, Taiwan, Republic of China)
Dual gate amorphous-indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with a bottom-gate covering the whole channel and a top-gate covering only a portion of the channel are investigated. The degree of degradation between the amorphous IGZO TFT using the dual gate-, top-gate only or bottom-gate only is compared. Under hot-carrier stress (HCS), the degradation of dual gate HCS is more significant than that of bottom-gate HCS. In addition, under negative gate bias illumination stress (NBIS), the threshold voltage after bottom-gate NBIS monotonically shifts in the negative direction, whereas top-gate NBIS operation exhibits on-state current increases without VT shift. Such anomalous degradation behavior of NBIS under top-gate operation is due to hole-trapping in the ESL above the central portion of the channel. These phenomena can be ascribed to the screening of the electric field by redundant source/drain electrodes. To understand the charge trapping rate in ESL, device with the different peak time of gate voltage under dynamic bias stress is also inspected.
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