高速铌酸锂电光调制器研究进展

薄膜铌酸锂调制器因其小尺寸、高带宽、低半波电压等优点,成为近年来业内关注的热点。文章梳理了铌酸锂电光调制器的波导结构、电极结构及偏置点控制技术三个方面的相关研究进展,分析了平面掩埋、脊型、光子晶体等三种不同结构波导的调制器性能,讨论了铌酸锂调制器集总和行波两种电极结构的特点及其设计考量因素,对比了电光调制器偏置点控制中功率法和导频法的优缺点及其相关研究成果。在此基础上,进一步分析了为实现更小体积与更高带宽铌酸锂调制器所需的关键技术以及未来的研究方向。     

Microstructure developments and anti-reflection properties of SiO2 films by liquid-phase deposition

In this work, silicon dioxide (SiO₂) films were deposited on a multi-crystalline silicon substrate via liquid-phase deposition (LPD) using hydrofluorosilicic acid (H₂SiF₆) and boric acid (H₃BO₃) aqueous solution. We controlled the surface morphology and grain structure of the film by using the concentration of H₂SiF₆, and the particle sizes were controlled by the concentration of H₃BO₃. Fourier transform infrared spectroscopy showed that three SiO_x peaks exist at 1103, 815, and 463 cm⁻¹, respectively. X-ray diffraction revealed a typical broad peak in the range of 14–55° for the SiO₂ amorphous particles. The refractive index of the LPD film was 1.41. The reflection of the LPD SiO₂ film was affected by the film thickness, and the reflectivity of the film was decreased as the film thickness increased. For the 106 nm SiO₂ film thickness, the average reflectance under the measuring conditions was 14.1%. The low reflectance rendered the film a suitable anti-reflection film in multi-crystalline silicon solar cells.     

Research of SiO2/InP structure prepared by photo-CVD

The SiO₂ film as an insulator in InP MOS structure was grown by mercury-sensitized photo induced chemical-vapor deposition (photo-CVD) utilizing gaseous mixture of monosilane (SiH₄) and nitrous oxide (N₄O) under 253.7 nm ultraviolet light irradiation. The PHOTOX SiO₂ film (i.e., SiO₂ film prepared by photo-CVD system) deposited at 250° C has a refractive index of 1.46 and breakdown field strength of 7.0 MV/cm. The 1 MHz capacitance-voltage characteristics of the InP MOS diode was measured to study the interface state densities. The minimum value is 1.2 × 10¹¹ cm⁻²eV⁻¹ for the sample prepared at a substrate temperature of 250° C.     

On the Relation between Morphology and FET Mobility of Poly(3‐alkylthiophene)s at the Polymer/SiO2 and Polymer/Air Interface

The influence of the interface of the dielectric SiO₂ on the performance of bottom‐contact, bottom‐gate poly(3‐alkylthiophene) (P3AT) field‐effect transistors (FETs) is investigated. In particular, the operation of transistors where the active polythiophene layer is directly spin‐coated from chlorobenzene (CB) onto the bare SiO₂ dielectric is compared to those where the active layer is first spin‐coated then laminated via a wet transfer process such that the film/air interface of this film contacts the SiO₂ surface. While an apparent alkyl side‐chain length dependent mobility is observed for films directly spin‐coated onto the SiO₂ dielectric (with mobilities of ≈10^?3 cm² V^?1 s^?1 or less) for laminated films mobilities of 0.14 ± 0.03 cm² V^?1 s^?1 independent of alkyl chain length are recorded. Surface‐sensitive near edge X‐ray absorption fine structure (NEXAFS) spectroscopy measurements indicate a strong out‐of‐plane orientation of the polymer backbone at the original air/film interface while much lower average tilt angles of the polymer backbone are observed at the SiO₂/film interface. A comparison with NEXAFS on crystalline P3AT nanofibers, as well as molecular mechanics and electronic structure calculations on ideal P3AT crystals suggest a close to crystalline polymer organization at the P3AT/air interface of films from CB. These results emphasize the negative influence of wrongly oriented polymer on charge carrier mobility and highlight the potential of the polymer/air interface in achieving excellent “out‐of‐plane” orientation and high FET mobilities.     

Effect of the film thickness on the crystal structure and ferroelectric properties of (Hf0.5Zr0.5)O2 thin films deposited on various substrates

In this work, the effect of the film thickness on the crystal structure and ferroelectric properties of (Hf_0.5Zr_0.5)O₂ thin films was investigated. The thin films were deposited on (111) Pt-coated SiO₂, Si, and CaF₂ substrates with thermal expansion coefficients of 0.47, 4.5, and 22×10⁻⁶/°C, respectively. From the X-ray diffraction measurements, it was found that the (Hf_0.5Zr_0.5)O₂ thin films deposited on the SiO₂ and CaF₂ substrates experienced in-plane tensile and compressive strains, respectively, in comparison with the films deposited on the Si substrates. For films deposited on all three substrates, the volume fraction of the monoclinic phase increased with increasing film thickness, with the SiO₂ substrate having the lowest monoclinic phase volume fraction at all film thicknesses tested. The grain size of the films, which is an important factor for the formation of the ferroelectric phase, remained almost constant at about 10 nm in diameter regardless of the film thickness and type of substrate utilized. Ferroelectricity was observed for the 17 nm-thick films deposited on SiO₂ and Si substrates, and the maximum remanent polarization (P_r) value of 9.3 µC/cm² was obtained for films deposited on the SiO₂ substrate. In contrast, ferroelectricity with P_r=4.4 µC/cm² was observed only for film on SiO₂ substrate in case of 55 nm-thick films. These results suggest that the films under in-plane tensile strain results in the larger ferroelectricity for 17 nm-thick films and have a ferroelectricity up to 55 nm-thick films.     

中频溅射技术制备镱铒共掺Al2O3光波导

在硅单晶(100)衬底上用热氧化法氧化一层SiO₂做缓冲层,在高纯铝靶上镶嵌金属Yb,Er,然后用中频磁控溅射法制备了镱铒共掺杂氧化铝薄膜。讨论了靶电压及沉积速率随氧流量的变化的磁滞回线效应,分析得出了沉积氧化物薄膜的最佳氧流量。在室温下检测到了薄膜的位于1535nm的很强的光致发光光谱(PL),并在光学掩模下用BCl₃离子束对薄膜样品进行刻蚀,得到条形光波导。     

Pulse Modulation of Multicolor Radiation Via Light Diffraction by Sound

Three acousto-optic materials, ТеО₂, SiO₂, and LiNbO₃, widely used in production of acousto-optic cells for pulse modulation of the multicolor optical radiation, have been compared. It is demonstrated that the ТеО₂ acousto-optic cell has an undoubted advantage in terms of the electric power consumption, first of all, due to its high acousto-optic figure of merit, while SiO₂ and LiNbO₃ cells are preferable from the viewpoint of the lowest distortions in transformation of electrical pulses into optical signals. Main theoretical conclusions have been confirmed by experiments on modulation of the multicolor Ar laser radiation.     

Study of high-quality epitaxial YBCO thin films grown directly on Y-Cut LiNbO3

Pulsed laser deposition was used to deposit high-quality YBa₂Cu₃O_7-δ (YBCO) thin films directly on y-cut LiNbO₃ substrates. The as-deposited YBCO films had a high degree of in-plane orientation and showed superconducting transition temperature (T_co) at 91K with a transition width of less than IK. Transport critical current densities were found to be ∼10⁶ A/cm² at 77K and zero field. An ion beam minimum channeling yield of 16% was obtained for YBCO films, indicating high crystallinity. High-resolution transmission electron microscopy studies showed that the interface between the film and the substrate was quite smooth and free from interfacial interdiffusion. The defects in thin films are also identified. The work showed that high-quality high T_c thin films can be deposited directly on LiNbO₃. Novel devices based on the properties of both YBCO and LiNbO₃ could be realized based on these results.     

光波导用MgO:LiNbO3晶体光学均匀性的测定

介绍了用非临界位相匹配温度法,测量了光波导用MgO:LiNbO3晶体光学均匀性的原理、公式和实际测量的结果.     

A non-polarization short-wave-pass thin film edge filter

Multilayer dielectric thin film edge filter has serious polarization sensitivity under oblique incidence. The cutoff-bands of the s-polarization and p-polarization light in conventional edge filter will separate obviously under 45° oblique inci- dence, which limits its application. Based on the two chosen materials TiO2 and SiO2, a novel stack structure is pro- posed to design the non-polarization short-wave-pass thin film edge filter. By using the （4H 4L 4H） as the matching layers, the polarization separation at 3 dB transmittance for the thin film edge filter cutoff-band is less than 1 nm at the incident angle of 45°. In this way, the non-polarization short-wave-pass edge filter is easily designed and fabricated.     

Quantum-well charge and voltage distribution in a metal–insulator–semiconductor structure upon resonant electron Tunneling

The prerequisites for electron storage in the quantum well of a metal–oxide–p ⁺-Si resonant-tunneling structure and the effect of the stored charge on the voltage distribution are theoretically investigated. Systems with SiO₂, HfO₂, and TiO₂ insulators are studied. It is demonstrated that the occurrence of a charge in the well in the case of resonant transport can be expected in structures on substrates with an acceptor concentration from (5–6) × 10¹⁸ to (2–3) × 10¹⁹ cm^–3 in the range of oxide thicknesses dependent on this concentration. In particular, the oxide layer thickness in the structures with SiO₂/p ⁺-Si(10¹⁹ cm^–3) should exceed ~3 nm. The electron density in the well can reach ~10¹² cm^–2 and higher. However, the effect of this charge on the electrostatics of the structure becomes noticeable only at relatively high voltages far above the activation of resonant transport through the first subband.     

Effect of the initial stage of film growth on device performance of organic transistors based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT)

The initial stage of organic film growth is considered to be vital for the carrier transport in organic thin-film transistors with bottom gate configuration. The same topographies of 40 nm dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) films on para-sexiphenyl (p-6P) monolayer and bare SiO₂ exhibited quite different field-effect mobilities, 1.9 and 0.1 cm²/V s, respectively. The further investigation indicated there were different growth behaviors at their initial stages of film growth. Column islands with high density were observed on SiO₂, while lamina islands on p-6P monolayer due to the good diffusion ability and their good epitaxial relationship. The latter is beneficial to obtain high quality film with less boundaries and defects. The work demonstrated that the initial stage of film growth is an important factor to determine the device performance of organic transistors, which is significant to improve the device fabrication and optimize the device performance.     

On the structure of low-temperature PECVD silicon dioxide films

It is demonstrated that the results of refractive index, infra-red absorption and electron spin resonance measurements on low temperature PECVD silicon dioxide films are con-sistent with a network structure composed of densified, amorphous SiO₂ and micro-scopes. The density of the amorphous SiO₂ is suggested to be greater than that of un-densified SiO₂ by about 10%. Approximately 5% of the deposited film volume is argued to consist of micropores High temperature annealing relaxes the dense state of the amorphous SiO₂ and collapses the volume occupied by the micropores.     

Sputtered oxides used for passivation layers of amorphous InGaZnO thin film transistors

Four sputtered oxide films (SiO₂, Al₂O₃, Y₂O₃ and TiO₂) along with their passivating amorphous InGaZnO thin film transistors (a-IGZO TFTs) were comparatively studied in this paper. The device passivated by an Al₂O₃ thin film showed both satisfactory performance (μ_FE=5.3 cm²/V s, I_on/I_off>10⁷) and stability, as was probably related to smooth surface of Al₂O₃ thin films. Although the performance of the a-IGZO TFTs with a TiO₂ passivation layer was also good enough (μ_FE=3.5 cm²/V s, I_on/I_off>10⁷), apparent V_th shift occurred in positive bias-stress tests due to the abnormal interface state between IGZO and TiO₂ thin films. Sputtered Y₂O₃ was proved no potential for passivation layers of a-IGZO TFTs in this study. Despite unsatisfactory performance of the corresponding a-IGZO TFT devices, sputtered SiO₂ passivation layer might still be preferred for its high deposition rate and excellent transparency which benefit the mass production of flat panel displays, especially active-matrix liquid crystal displays.     

Facile embedding of SiO2 nanoparticles in organic solar cells for performance improvement

In this paper, performance improvement of organic solar cells (OSCs) via facile embedding of SiO₂ nanoparticles is reported. Both experimental and theoretical studies indicate that the improved performance is mainly owed to the increased short circuit current density (J_sc), which can be further attributed to elongated optical path length and thus to enhanced light confinement caused by light scattering of SiO₂ nanoparticles. Compared to the planar reference device with a structure of ITO/PEDOT:PSS/P3HT:PC₆₁BM/Al, the optimized one embedded with 160-nm-diameter SiO₂ nanoparticles exhibits ∼17.5% increase in J_sc, i.e., from 10.30 to 12.10 mA/cm², leading to the resultant performance improvement. Owing to the unique advantages of SiO₂ nanoparticles including electrical insulation, low cost and easy fabrication, valuable guidelines for fabricating the related high performance-to-cost OSCs can be provided by this study.     

Ohmic contacts to InP-based materials induced by means of rapid thermal low pressure (metallorganic) chemical vapor deposition technique

A rapid-thermal-low-pressure-metallorganic-chemical-vapor-deposition (RT-LPMOCVD) technique was executed in order to deposit non-semiconductor thin layer materials, necessary for producing metal contact to InP-based microelectronic devices. Silicon dioxide (SiO₂) films were deposited onto InP substrates in rapid thermal cycles, using O₂ and 2% diluted SiH₄ in Ar, with very fast growth kinetics and low activation energy. The SiO₂ film exhibited excellent properties, such as refractivity index, density, internal stress, and wetp-etch rates. The SiO₂ films were dry etched in a given pattern to allow for the formation of a small metal contact to the InP-based material, onto which the SiO₂ layer was deposited. Subsequently, titanium-nitride (TiN _x ) thin films were deposited onto the InP substrate through rapid thermal deposition cycles, using a tetrakis (dimethylamido) titanium (DMATi) metallorganic liquid source as the precursor for the process, with fast kinetics. The deposited TiN _x films had a stoichiometric structure and contained nitrogen and titanium in a ratio close to unity, but incorporated a large amount of carbon and oxygen. The film properties, such as resistivity (40–80 μΩ·mm) and stress (compressive; ?0.5 to ?2.0×10⁹ dyne·cm^?2), were studied in addition to an intensive investigation of its microstructure and morphology, and their performance as an ohmic contacts while deposited ontop?In_0.53Ga_0.47As material (Zn doped 1.2×10¹⁸ cm^?3).     

Electroluminescence mechanisms in SiO x N y (Si) nanocomposite films

With a view to creating the Si LED, the mechanisms of electroluminescence (EL) in SiO_xN_y(Si) nanocomposite films with Si nanocrystals embedded in the SiO_xN_y matrix are studied experimentally and theoretically. The most important results are obtained from a Au/SiO_xN_ySi)/p-Si structure having a semitransparent electrode, the oxynitride film containing Si nanocrystals with a mean size of 3–5 nm and a concentration of ～10¹⁸ cm^?3; the measurements are made on a reverse-biased structure (substrate potential negative). Room-temperature EL is observed in the visible and IR ranges; the respective peaks are located at wavelengths of 600–700 and about 1200 nm. The study examines current-voltage characteristics of the structure and the dependence of integrated EL intensity on current, voltage, film thickness, the type of substrate conductivity, etc. The following conclusions are drawn from the experimental and theoretical results: The IR branch is mainly associated with carrier heating, avalanche ionization, and formation of light-emitting microplasmas near the substrate-film interface. The visible branch is linked to (i) hot-electron injection from the substrate into the film and (ii) impact excitation of luminescent centers at nanocrystal-matrix interfaces.     

The development of an 850 GHz waveguide receiver using tuned sis junctions on 1µm Si3N4 membranes

We report preliminary development work on a 850 GHz SIS heterodyne receiver employing a tuned niobium tunnel junction on a 1 µm Si₃N₄ supporting membrane. Since the mixer is meant to be operated well above the superconducting gap frequency of niobium (2δ/h ? 690 GHz) special care has been taken to minimize transmission line loss. We have therefore used junctions with an integrated radial stub RF matching network to tune out the large shunt susceptance of the junction and minimize the niobium film absorption loss. Scale model measurements of the waveguide embedding impedance have been made to aid in the design of the choke structure and RF matching network. Detailed Fourier Transform Spectrometer measurements of tuned junctions on both SiO₂ and silicon nitride membranes show response up to 1100 GHz and indicate that the absorption loss in the niobium film is in the order of 4–7 dB at 850 GHz, in fairly good agreement with the theoretical loss calculated from the Mattis-Bardeen theory. The junctions have a center frequency of 800 GHz which presents a 6% downshift from the designed value.     

Chalcogenide glasses as passive thin film structures for integrated optics

One approach to obtaining electro-optic or magneto-optic modulation in an integrated optic structure is to use a transparent film on an “active” (electro- or magneto-optic) optical substrate. Since the most useful active optical materials have relatively high refractive indices which preclude the use of oxide glasses as the transparent thin film, we have investigated the possibility of using higher index chalcogenide glasses in this configuration. Preliminary waveguiding studies were performed on a model system consisting of an As₂S₃ film on a LiNbO₃ substrate which demonstrated the feasibility of using chalcogenide glasses in this regard. The optical and mechanical properties of a suitable glass system, As-Ge-S, were then characterized. The characterization consisted of developing empirical formulas based on the type of bonding present in the glass which can be used to predict the relevant properties of a glass as a function of its composition. These formulas allow selection of optimum glass compositions to match a variety of electro-optic and magneto-optic substrates.     

Fully depleted silicon on insulator MOSFETs on (1 1 0) surface for hybrid orientation technologies

Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices needs good TFT characteristics. The reduction in leakage current of the TFT devices was accomplished with the gate offset (GOF) structure. A simplified fabrication process for the GOF NVM is introduced in this study using the insulator over-etching approach. Nonvolatile memory devices on glass using SiO₂/SiO_x/SiO_xN_y stack with an offset length of 0, 0.2, 0.4, and 0.6 μm were investigated. The highly selective etching process and the short offset length help to avoid the problem of the gate aluminum collapsing on the source/drain electrodes. The TFT characteristics of the GOF structures displayed the remarkable improvement in leakage from 1.1 × 10⁻¹¹ A, for the TFT without an offset region, to the low OFF current of 1.34 × 10⁻¹² A for the device with a 0.6 μm offset length. The longer offset length gave the lowest OFF current. The degradation in transconductance and the threshold voltage was negligible with the g_m values of about 3 × 10⁻⁶ S and ΔV_th of about 0.2 V, respectively. The switching characteristics remained similar for all the devices. Additionally, the GOF structures slightly enhanced the retention characteristics. The memory window of the NVM without the offset after a retention time of 10,000 s was 58%, lower than the over 69% of the GOF devices. Therefore, the application of the GOF structure to reduce the leakage of the NVM/TFT proved to be effective.