High-k Dielectric Thin Films Research Articles

Electronic Properties of Atomic Layer Deposited HfO2 Thin Films on InGaAs Compared to HfO2/GaAs Semiconductors

This paper demonstrates how the treatment of III-V semiconductor surface affects the number of defects and ensures the conformal growth of the high-k dielectric thin film. We present the electrical properties of an HfO2/InGaAs-based MOS capacitor, in which growth temperatures and surface treatments of the substrate are two key factors that contribute to the uniformity and composition of the HfO2 thin films. A remarkable asymmetry observed in capacitance versus voltage measurements was linked to the interface defects and charge redistribution, as confirmed from X-ray photoelectron spectroscopy. The GaAs substrates that were etched with only NH4OH showed a large frequency dispersion and a higher surface roughness; however, the HfO2 thin films grown on GaAs pre-treated with both NH4OH etching and (NH4)2S passivation steps produced a desirable surface and superior electronic properties.

High-k dielectric based high performance vertical organic thin film transistor for flexible low power applications

The basic performance parameters such as threshold voltage, drain current and saturation mobility play an important role for any transistor-based devices. The planar organic TFT provides a good performance but it is still not satisfactory. Therefore, in this paper, a vertical channel TFT (D5) is proposed that exhibits a significant improvement for threshold voltage V t , drain current I Dmax and saturation mobility μ sat in comparison to planar devices. The proposed vertical device (D5) is 44 and 24 times enhanced in comparison with planar device D1 in terms of I Dmax and μ sat , correspondingly. Furthermore, this paper compares five different vertical-channel device architectures (D2, D3, D4, D5, D6 & D7). Out of these structures, our proposed novel structure (D5) shows remarkable performance in terms of drain current (528 μA) and saturation mobility (80.8 cm2/V.s). As compared to the best mentioned vertical devices D2, D3 and D7, the proposed device exhibits 41.8 %, 15.6 % and 27.8 %, increment in drain current, respectively. Additionally, the proposed device exhibits about 2.7, 5.2 and 3.5 times improvement in comparison with D2, D3 and D7 correspondingly. The reasons for this better performance of the proposed device have been explained by vertical and horizontal cutline analysis.

Modulation of electrical properties of sputtered Ta2O5 films by variation of RF power and substrate temperature

Dielectric thin films are important building blocks of microelectronic devices, and hence, research on the development of high-k dielectric thin films has drawn tremendous research interest. In this research, thin films of tantalum oxide (Ta2O5), a high-k dielectric material, are deposited on the Si substrate by the radio frequency (RF) magnetron sputtering technique. During the deposition of Ta2O5 thin film, the sputtering parameters such as sputtering power and substrate temperature were systematically varied, and post-deposition structural, morphological, and electrical properties of sputtered Ta2O5 films are studied by x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscope, capacitance–voltage (C-V) and current–voltage (I-V) measurement techniques. The annealed Ta2O5 thin film at the temperature of 900 °C for 1 h possesses polycrystalline nature with β—phase orthorhombic crystal structure. The film deposited at 150 W and substrate temperature at room temperature has shown comparatively lower surface roughness, which depicts the energy, and mobility of adatoms greatly influenced by RF power and substrate temperature. With the increase in sputtering power, the oxide charge density (Qox) is found to increase. On the other hand, Qox is found to decrease with the increase in substrate temperature. The film deposited at RF power of 150 W and substrate temperature of 300 °C is found to be of high dielectric constant, low oxide and interface charge density, and lower leakage current.

Role of Cyclopentadienyl Ligands of Group 4 Precursors toward High-Temperature Atomic Layer Deposition

Deposition of high-k dielectric thin films is essential for manufacturing modern electronic devices. Atomic layer deposition (ALD) is an attractive technology for depositing high-k materials because it exhibits conformality and facilitates thickness control of the films at the atomic level. It has been suggested that high-temperature ALD can enhance the material properties of the deposited films such as density and crystallinity, for which the development of thermally stable precursors that deliver the metallic element is required. Heteroleptic titanium (Ti), zirconium (Zr), and hafnium (Hf) precursors containing amido and cyclopentadienyl (Cp) ligands have recently been introduced, with some demonstrating improved thermal stability. However, the mechanism behind the improved thermal stability of these precursors remains unclear. This research employs density functional theory (DFT) calculations to elucidate the role of Cp ligands of group 4 (Ti, Zr, Hf) precursors for high-temperature ALD. The surface adsorption reactions of the precursors on oxide surfaces are suggested to be facile. For most precursors, one or two ligands are thought to exist after chemical adsorption. Cp ligands, in particular, are expected to persist on the surface, whereas amido ligands are more easily eliminated during adsorption. The decomposition of the precursor after adsorption on the surface then is considered, for which the thermal stability is significantly enhanced by introducing the Cp ligand. Furthermore, precursors with Cp ligands are more difficult to adsorb on the partially decomposed precursor-on-surface. Our findings intend to offer a fundamental molecular-level understanding of the thermal stability of group 4 precursors for high-temperature ALD.

Novel Al1.997Hf0.003O3 High-k gate dielectric thin films grown by pulsed laser deposition using pre-synthesized target material

The present study reported pure pre-synthesized Al1.997Hf0.003O3 target for the formation of novel high-k gate dielectric thin films using pulsed laser deposition technique. High substrate temperature of 800 °C and ultra-high-vacuum condition at 10−8 Torr were used to produce stable hexagonal crystal structure of thin films with exclusive crystal growth directions in the (110) and (024) planes as evidenced by the XRD. AFM images displayed dense and uniform distribution of crystallites with RMS as low as 0.12 nm, contributing to very smooth morphology. Optical observation by the UV–Vis analysis showed that the introduction of Hf in the lattice of the Al2O3 material had significantly modified the energy bands of Al1.997Hf0.003O3, hence, improved k values. Consequently, the C–V measurements of the fabricated thin films based on Pt/Al1.997Hf0.003O3/p-Si MOS capacitor exhibited a high capacitance of ~ 202 nF at ~ 6 nm thickness and attributed to high-k value of ~ 21. The I–V measurements also revealed the electron tunnelling was reduced with thicker films of Al1.997Hf0.003O3, due to this, leakage current density was improved to ~ 10−10 A/cm2. These results revealed that Al2−xHfxO3 thin films could be significant in searching for a replacement dielectric for nanoscale MOS devices.

Surface functionalization toward top-gated monolayer MoS2 field-effect transistors with ZrO2/Al2O3 as composite dielectrics

Growth of high-k dielectrics on two-dimensional (2D) materials is vital for the fabrication of electronic and optoelectronic devices. In this work, the uniform high-k ZrO2 dielectric thin films were successfully grown by atomic layer deposition (ALD) on monolayer MoS2 with Al2O3 buffer layers. No significant variations appear for MoS2 after deposition of Al and ZrO2 thin films. The properties of composite dielectrics on MoS2 films have been studied by Cr-Au/ZrO2/Al2O3/MoS2 Metal-oxide-semiconductor (MOS) devices, in which H2O and O3 were used as the oxidants for ZrO2 growth, respectively. Moreover, the top-gated monolayer MoS2 field-effect transistors (FETs) with ZrO2/Al2O3 as composite dielectrics have been successfully fabricated. Importantly, the top-gated structure gives the transistors with a high mobility of 11.14 cm2 V−1 s−1, a high on/off-state current ratio of 107 at VDS = 0.1 V, a small subthreshold swing of 0.93 V dec−1, and a proper threshold voltage of 2.29 V. Hence, the integration of the high-k dielectrics on MoS2 develops the possibilities to prepare high-performance top-gated FETs based on 2D materials.

CMOS-compatible synaptic transistor gated by chitosan electrolyte-Ta2O5 hybrid electric double layer

This study proposes a hybrid electric double layer (EDL) with complementary metal-oxide semiconductor (CMOS) process compatibility by stacking a chitosan electrolyte and a Ta2O5 high-k dielectric thin film. Bio-inspired synaptic transistors with excellent electrical stability were fabricated using the proposed hybrid EDL for the gate dielectric layer. The Ta2O5 high-k dielectric layer with high chemical resistance, thermal stability, and mechanical strength enables CMOS-compatible patterning processes on biocompatible organic polymer chitosan electrolytes. This technique achieved ion-conduction from the chitosan electrolyte to the In-Ga-Zn oxide (IGZO) channel layer. The on/off current ratio, subthreshold voltage swing, and the field-effect mobility of the fabricated IGZO EDL transistors (EDLTs) exhibited excellent electrical properties of 1.80 × 107, 96 mV/dec, and 3.73 cm2/V·s, respectively. A resistor-loaded inverter was constructed by connecting an IGZO EDLT with a load resistor (400 MΩ) in series. This demonstrated good inverter action and responded to the square-wave input signals. Synaptic behaviours such as the hysteresis window and excitatory post-synaptic current (EPSC) variations were evaluated for different DC gate voltage sweep ranges and different AC gate spike stimuli, respectively. Therefore, the proposed organic–inorganic hybrid EDL is expected to be useful for implementing an extremely compact neural architecture system.

Laser Ablation Ceramic Target for 8YSZ High-k Dielectric Electrolyte thin Films Precessed by PLD on Si(100) and Pt/Si(111)

The cubic structure 8YSZ (8%Yttria-Stabilized Zirconia) thin films deposited by PLD(Pulsed Laser Deposition) on substrates Si (100) and Pt/Si (111) by identical control parameters have potential applications as electrolytes for planar micro electrochemical devices like Lambda oxygen sensors and IT-�SOFC. It appearance differences in polycrystalline structural and optical characterization by XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), AFM (Atomic Force Microscopy) and V- VASE (Variable Angle Spectroscopic Ellipsometry. The differences are relating on crystalline dimensions, lattice parameters; surface roughness measured by V- VASE and AFM are presented synthetic to evidence the differences generated by substrates.

Influence of high energy ion irradiation on structural, morphological and optical properties of high-k dielectric hafnium oxide (HfO2) thin films grown by atomic layer deposition

Abstract Modifications and resulting changes in various properties of nanocrystalline HfO2 high-k dielectric thin films with nominal thickness of 20 nm grown by atomic layer deposition technique on silicon and glass substrates were investigated as a function of swift heavy ions (SHI) irradiation. In the present work, our attention is to study the electronic excitation induced modifications in HfO2 thin films cause of formation of defects by 120 MeV Au9+(SHI) irradiation. For the same purpose, the annealed (500 °C) HfO2 thin films were irradiated with the varying fluence in the range of 1E11 to 1E13 ions/cm2. The virgin and irradiated representative HfO2 thin films were investigated by various techniques. The substantial root mean square (RMS) surface roughness (0.5–1 nm) and variation in grain size (40–52 nm) as a function of Au9+ ions irradiation were determined using atomic force microscope (AFM). The optical properties of HfO2 thin films were analyzed by measuring absorbance and transmission (54–62%) spectra in 200–700 nm wavelength range followed by calculation of optical band gap (Eg). The photoluminescence (PL) spectra obtained at excitation wavelength 220 nm indicate the formation of defects due to SHI irradiation. A change in excitation wavelength (220–260 nm) causes the shift in emission peaks towards higher wavelength. Structural investigations have been carried by Grazing Incidence X-ray Diffraction (GIXRD) techniques which reveal the variation in crystallite size as a function of different fluence. The results of a systematic XPS study of virgin and SHI irradiated samples shows the shifting of Hf 4f and O 1s peaks towards lower binding energy as compared to virgin sample. O K-edge XANES were performed to understand the ion-beam irradiation induced defect formation and their consequences on the electronic structure of HfO2 thin films. The obtained peaks in Rutherford backscattering spectrometry (RBS) affirm the existence of Hf and O elements and width of the peaks determine the sample thickness (20 nm).

High energy (150 MeV) Fe11+ ion beam induced modifications of physico-chemical and photoluminescence properties of high-k dielectric nanocrystalline zirconium oxide thin films

Abstract This work presents the influence of dominated electronic energy loss over nuclear energy loss induced by swift heavy ion (SHI) irradiation on the physico-chemical, optical and other properties of RF grown zirconium oxide (ZrO2) thin films. For this purpose, thin films of ZrO2 grown on glass substrate were irradiated by 150 MeV Fe11+ ions with a range of fluence from 2E12 to 5E13 ions/cm2 to understand the mechanism of induced modifications and defects generation. The XRD results confirmed that the virgin and irradiated ZrO2 thin films were crystalline in nature with monoclinic and tetragonal structure. The crystallite size varied from 19.93 nm to 46.43 nm with varying ion fluence. Strain, dislocation density and stacking fault were used to investigate the changes in structural parameters. Tauc's plot method was employed for the quantitative evaluation of optical energy band gap (Eg) that exist in the range of 4.45–4.62 eV. The transmittance (%) of the virgin and Fe11+ ions irradiated samples was determined in the range of 35.69–66.09% using UV–Vis. spectroscopy. Further, the refractive index was determined using different methods significantly depends on the optical band gap. The broad PL emission peaks were obtained at 375 nm and 440 nm with the excitation wavelength (λex.) of 300 nm. The variation in PL intensity with increasing ion fluence was attributed to the creation or annihilation of primary or complex defects. FTIR spectroscopy was employed for the analysis of chemical modifications in vibrational bonds of samples and the band obtained 660 cm−1was assigned to the asymmetrically coupled Zr–O–Zr stretching which presents the strong vibration in samples. The band intensity increased up to the fluence 5E12 ions/cm2 and decreased at a higher fluence of 1E13 ions/cm2. Rutherford backscattering spectroscopy technique was used to determine the thickness (165 nm) of the samples.

Atomic-layer-deposited (ALD) Al2O3 passivation dependent interface chemistry, band alignment and electrical properties of HfYO/Si gate stacks

In this work, the effects of atomic-layer-deposited (ALD) Al2O3 passivation layers with different thicknesses on the interface chemistry and electrical properties of sputtering-derived HfYO gate dielectrics on Si substrates have been investigated. The results of electrical measurements and X-ray photoelectron sepectroscopy (XPS) showed that 1-nm-thick Al2O3 passivation layer is optimized to obtain excellent electrical and interfacial properties for HfYO/Si gate stack. Then, the metal-oxide-semiconductor capacitors with HfYO/1-nm Al2O3/Si/Al gate stack were fabricated and annealed at different temperatures in forming gas (95% N2+5% H2). Capacitance-voltage (C-V) and current density-voltage (J-V) characteristics showed that the 250 °C-annealed HYO high-k gate dielectric thin film demonstrated the lowest border trapped oxide charge density (-3.3 × 1010 cm−2), smallest gate-leakage current (2.45 × 10-6 A/cm2 at 2 V) compared with other samples. Moreover, the annealing temperature dependent leakage current conduction mechanism for Al/HfYO/Al2O3/Si/Al MOS capacitor has been investigated systematically. Detailed electrical measurements reveal that Poole-Frenkle emission is the main dominant emission in the region of low and medium electric fields while direct tunneling is dominant conduction mechanism at high electric fields.

Analysis of the electrical properties and current transportation mechanism of a metal oxide semiconductor (MOS) capacitor based on HfGdO gate dielectrics

The microstructure, optical and electrical properties of sputtering-derived HfGdO high-k gate dielectric thin films as a function of the Gd doping content have been systematically investigated. X-ray diffraction (XRD) measurements have indicated that Gd doping can form a new stable cubic phase. The optical band gap of the HfGdO gate dielectrics increases gradually from 5.82 to 6.14 eV as the Gd doping concentration increases. The electrical properties, such as permittivity, oxide trapped charge density, border trap charge density and leakage current density of samples, are determined using a semiconductor device analyzer. The formation mechanism of leakage current is also discussed in detail. In addition, the interfacial properties of HfGdO/Si gate satcks were tested to establish the electrical properties. The excellent optoelectronic properties, such as the optical band gap of 5.95 eV, leakage current density of 8.33 × 10−8 A/cm2 at a bias voltage of 2 V, oxide trapped charge density of −1.06 × 1012 cm−2 and a border trap charge density of zero and optimized interfacial properties were observed in the HfGdO thin films with sputtering power of 30 W, indicating that it may become a potential high-k gate dielectric in future complementary metal oxide semiconductor (CMOS) devices.

Modulation of the microstructure, optical, and electrical properties of HfYO gate dielectrics by annealing temperature

In this study, Y-doped HfO2 (HYO) high-k gate dielectric thin films have been deposited on cleaned n-type Si wafers by using co-sputtering technique. Annealing temperature dependent structural, optical, interfacial and electrical properties of HYO have been systemically studied using the x-ray diffraction (XRD), ultraviolet–visible spectroscope (UV–Vis), spectroscopy ellipsometry (SE), x-ray photoelectron spectroscopy (XPS) and electrical measurements. Based on XRD measurements, it can be noted that cubic phase has been detected and remained while doping with yttrium element and annealing at high temperature. Optical analysis by SE indicates that incorporation of Y into HfO2 can enlarge the band gap and decrease the refraction index of the samples. High temperature annealing leads to the formation of low-k SiO2 layer and silicate. Electrical measurements have demonstrated that MOS capacitor based on HYO/Si gate stack annealed at 400 °C shows excellent electrical properties, such as high dielectric constant, low oxide charge density border trapped oxide charge density and leakage current density, which can be attributed to the increase in band gap and conduction band offset by Y incorporation.

Solution-processed HfGdO gate dielectric thin films for CMOS application: Effect of annealing temperature

Annealing temperature dependent microstructure, optical and electrical properties of sol-gel-deposited HfGdO high-k gate dielectric thin films on Si substrates are systematically investigated. X-ray spectroscopy (XPS) analyses have confirmed that the interfacial layer at HfGdO/Si interface is mainly silicate and the component increases with increasing the annealing temperature. Moreover, the band offsets for HfGdO/Si gate stack as a function of annealing temperature also have been determined. As a result, it can be noted that increase in valence band offset (ΔEv) and reduction in conduction band offset (ΔEc) have been detected. Electrical characterizations have indicated that higher annealing temperature effectively improves the electrical characteristics, such as the increased effective permittivity (k) and the decreased flat band voltage shift (ΔVfb). However, due to the reduced ΔEc and the appearance of crystallization, increased leakage current density has been observed with the increase in annealing temperature.

(Invited) Amorphous Zr-Doped HfO2 high-K Dielectric Thin Film for Electronic and Optoelectronic Applications

Metal oxides have been used as the high-k dielectric materials in ICs and TFTs for several decades. Recently, they are used as the gate dielectric in the nano-sized MOSFET to take the advantage of the low leakage current and other device properties. HfO2 is the most popular high-k gate dielectric for sub 1 nm EOT transistors and circuits. One of its main drawbacks is the low crystallization temperature, i.e., < 700°C, which can be a serious reliability problem. We have solved this problem by adding Zr into HfO2 to form the Zr-doped HfO2 (ZrHfO) film. This kind of high-k film can remain amorphous after been heated to above 900ºC. The material and electrical properties can be optimized by controlling the concentration of Zr in the film and the post deposition annealing (PDA) condition. In this talk, the author reviews his works in dielectric and non-dielectric applications of the amorphous ZrHfO thin film. They are highly dependent on the structure of the film. The amorphous ZrHfO high-k thin film can be transformed into heterogeneous structures for non-dielectric applications. For example, one or more of the nanocrystalline materials have been embedded into the ZrHfO thin film to serve as charge trapping media. Electrons and holes can be stored in this kind of film separately with the selection of the proper nanocrystal materials and the gate bias condition. This kind of nonvolatile memory device has a lifetime more than 10 years The amorphous ZrHfO high-k thin film can be prepared into another type of heterogeneous structure. After the hard breakdown process, many nano-resistors can be permanently and uniformly formed in the high-k thin film. Light can be emitted from nano-resistors upon the application of a voltage. This is a solid state incandescent light emitting device (SSI-LED) became the principle of light emission is the black body emission. The emitted light has the broad-band spectrum covering the whole visible and part of the near-IR wavelength range. Applications of SSI-LEDs include lighting, on-chip optical interconnect, and others. The nano-resistor structure can also be used as one-time-programmed memory devices, i.e., antifuses, because the leakage current ratio after and before the breakdown process can be larger than 105. Separately, the nano-resistor structure has the current rectification function, which makes it a diode device. However, different from the on-off function of the conventional p-n junction diode, which has a drastic change of the current upon a small increase of the driving voltage, the nano-resistor based diode has the gray-scale capability because of the gradual change of the current vs. voltage curve. There are many other possible applications of the amorphous ZrHfO high-k thin film beyond the conventional electronics and optoelectronics, which will also be discussed. This talk is dedicated to the memory of Prof. Samares Kar for his seminal contribution to this important ECS symposium series.

Using Dopants to Tune Oxygen Vacancy Formation in Transition Metal Oxide Resistive Memory.

Introducing dopants is an important way to tailor and improve electronic properties of transition metal oxides used as high-k dielectric thin films and resistance switching layers in leading memory technologies, such as dynamic and resistive random access memory (ReRAM). Ta2O5 has recently received increasing interest because Ta2O5-based ReRAM demonstrates high switching speed, long endurance, and low operating voltage. However, advances in optimizing device characteristics with dopants have been hindered by limited and contradictory experiments in this field. We report on a systematic study on how various metal dopants affect oxygen vacancy formation in crystalline and amorphous Ta2O5 from first principles. We find that isoelectronic dopants and weak n-type dopants have little impact on neutral vacancy formation energy and that p-type dopants can lower the formation energy significantly by introducing holes into the system. In contrast, n-type dopants have a deleterious effect and actually increase the formation energy for charged oxygen vacancies. Given the similar doping trend reported for other binary transition metal oxides, this doping trend should be universally valid for typical binary transition metal oxides. Based on this guideline, we propose that p-type dopants (Al, Hf, Zr, and Ti) can lower the forming/set voltage and improve retention properties of Ta2O5 ReRAM.

The Application of a Selective Etch to Conclusively Show the Surface Smoothing Effect of an Amorphous Thin Film Deposited by Atomic Layer Deposition

It can be predicted by theory that the atomic layer deposition (ALD) of an amorphous high-k dielectric thin film on a rough bottom metal electrode has a surface smoothing effect, resulting in a smoother top surface. This effect can strongly affect the electrical characteristics of high-k MIM capacitors. Sometimes this effect may be hard to observe by atomic force microscopy (AFM) because the bottom metal electrode may be modified by the ALD process, resulting in an apparently contradictory AFM measurement. The solution is to use a chemically and physically stable metal with a Hüttig temperature larger than the ALD temperature. In addition, AFM after a selective etch is very useful in order to demonstrate the surface smoothing effect by ALD conclusively.

Low-temperature solution-based fabrication of high-k HfO2 dielectric thin films via combustion process

HfO2 dielectric is one potential material in advanced microelectronics. Its solution-based fabrication usually requires high annealing temperature to remove residual organic solvent, which limits its applications in flexible electronics. Here a low-temperature and solution-processed high-k HfO2 dielectric was demonstrated. With the assistance of combustion process, amorphous HfO2 films were realized at annealing temperature below 300 °C. XRD, Raman and XPS analyses indicated structural and crystalline properties. Electrical measurements indicated that the films showed leakage current density lower than 5.8 × 10−8 A/m2 at 100 MV/m and breakdown field larger than 500 MV/m. Such low-temperature-processed films were expected to be integrated as high-quality gate dielectric in flexible electronics. Via the assistance of citric acid-based combustion method, solution-processed amorphous HfO2 dielectric films were realized at relatively low annealing temperature below 300 °C. Films showed smooth surfaces and good dielectric and breakdown properties

Filter of SSI-LED Light Using Thin Films

Recently, Kuo and Lin presented a new-type of solid state incandescent light emitting device (SSI-LED) that was made from a MOS structure with a high-k dielectric thin film, such as the Zr-doped HfO2 (ZrHfO) [1-3]. This kind of device emits the warp white light from the thermal excitation of nano-sized conductive paths surrounded by the dielectric film during the passage of a large current [4]. The emitted light covers the visible to near-IR wavelength range similar to that emitted from an incandescent light bulb [4]. The device was fabricated using the IC compatible process. Possible applications of the SSI-LED include displays, sensors, and in-chip optical interconnects [5]. For certain applications, such as the short distance optical interconnect, the wavelength has to be around 850-900 nm [67], which is within the wavelength range of the light emitted from the SSI-LED. It is also suitable for the light sensing using the Si diode [7]. A proper thin film light filter may be used for this purpose. In this paper, PECVD SiNx and a-Si:H thin films were examined for the light filtration of the light emitted from the SSI-LED made of the ZrHfO high-k dielectric. A 200 nm thick SiNx film was deposited on the dilute HF cleaned p-type Si (100) wafer and wet-etched into 250 µm diameter holes. A ZrHfO film was sputter-deposited on the substrate from a ZrHf (12/88 wt. %) target for 12 min in Ar/O2 (1:1) at 5 mTorr and 60 W. Then, an ITO film was sputter deposited on top of the ZrHfO film and wet etched into gate electrodes, which were connected to contact pads at the edge of the substrate through metal lines composed of Mo (200 nm)/Al (120 nm). The backside of the wafer was deposited with Mo to form the ohmic contact. The post metal annealing was done in a forming gas at 250°C for 5 min. The light emission spectrum of the SSI-LED was measured at the gate voltage (Vg ) of -20 V. Subsequently, the device was coated with a film of a 200 nm thick SiNx or a 6.5 nm thick a-Si:H deposited by PECVD. The spectrum of the light emitted from the same SSI-LED coated with the thin film was measured. Spectra of the same device with and without the filter were compared. Figure 1 shows the normalized light emission spectra of the SSI-LED before and after coating with the SiNx film. Before the SiNx coating, the light emission spectrum covers the wavelength range of 480 nm to 900 nm with the peak located at 700 nm. It is similar to spectra of typical SSI-LEDs without any filter [1-4]. However, when coated with the SiNx film, the shape of the spectrum changed. None of the light below 500 nm wavelength is detected. The spectrum contains two peaks at around 550 nm and 720 nm. The light above 750 nm wavelength drops, which becomes more obvious with the increase of the wavelength. The spectrum of the SiNx filtered SSI-LED is similar to the light transmission spectrum of the SiNx film [8]. The strong light absorption of SiNx at 600-650 nm and 900-1000 nm wavelength ranges contributes to the dual-peak spectrum in Fig. 1. Figure 2 shows the normalized light emission spectra of the SSI-LED before and after coating with an a-Si:H film. After coating with the a-Si:H film, the light emission spectrum shifted toward the long wavelength direction, i.e., from the peak of 700 nm to 750 nm. The intensity of the light in the 480 to 580 nm range dropped to zero. Previously, it was reported that the a-Si:H film strongly absorbed the short wavelength light in the 300 nm to 600 nm range [9]. Fig. 2 shows that the SSI-LED light below 650 nm is totally absorbed by the top a-Si:H film. In summary, the broad band light emitted from the SSI-LED can be filtered to a narrow wavelength range with a deposited thin film. [1] Y. Kuo and C.-C. Lin, APL, 102, 031117 (2013). [2] Y. Kuo and C.-C. Lin, ESSL, 2, Q59 (2013). [3] Y. Kuo and C.-C. Lin, SSE, 89, 120 (2013). [4] Y. Kuo, IEEE TED, 62, 3536 (2015). [5] Y. Kuo, ECS Tran., 54, 273 (2013). [6] D. A. B. Miller, IEEE Proc., 88(6), 728 (2000). [7] S. Radovanovic et al, High-Speed Photodiodes in Standard CMOS Technology, p. 24 (2006). [8] A. M. Perez et al, Opt. Eng., 45, 123801 (2006). [9] X. Li et al, Opt. Express, 21, A677 (2013). Figure 1

Microstructure, optical and electrical properties of sputtered HfTiO high-k gate dielectric thin films

The microstructure, optical and electrical properties of HfTiO high-k gate dielectric thin films deposited on Si substrate and quartz substrate by RF magnetron sputtering have been investigated. Based on analysis from x-ray diffraction (XRD) measurements, it has been found that the as-deposited HfTiO films remain amorphous regardless of the working gas pressure. Meanwhile, combined with characterization of ultraviolet-visible spectroscopy (UV–vis) and spectroscopy ellipsometry (SE), the deposition rate, band gap and optical properties of sputtered HfTiO gate dielectrics were determined. Besides, by means of the characteristic curves of high frequency capacitance–voltage (C–V) and leakage current density–voltage (J–V), the electrical parameters, such as permittivity, total positive charge density, border trap charge density, and leakage current density, have been obtained. The leakage current mechanisms are also discussed. The energy band gap of 3.70eV, leakage current density of 1.39×10−5A/cm2 at bias voltage of 2V, and total positive charge density and border trap charge density of 9.16×1011cm−2 and 1.3×1011cm−2, respectively render HfTiO thin films deposited at 0.6Pa, potential high-k gate dielectrics in future CMOS devices.