Polyimide/Ta2O5/polyimide antiresonantreflecting optical waveguides

A novel antiresonant reflecting optical waveguide (ARROW) fabricated using both the organic and dielectric thin film technologies is presented for the first time. The ARROW consisted of the fluorinated polyimide and tantalum pentoxide (Ta₂O₅) hybrid layers deposited on a Si substrate. For TE polarized light, the propagation loss of the waveguide as low as 0.8 dB/cm is obtained at 632.8 nm. The propagation loss for TM polarized light is 2.7 dB/cm. Some design considerations of the hybrid ARROW are also discussed in this work     

Low-loss polyimide-Ta2O5-SiO2hybrid ARROW waveguides

A low-loss polyimide-Ta₂O₅-SiO₂ hybrid antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW device was fabricated using both the organic and dielectric thin-film technologies. It consists of the fluorinated polyimide, tantalum pentoxide (Ta₂O₅), and silicon dioxide (SiO₂) hybrid layers deposited on a Si substrate. For transverse electric polarized light, the propagation loss of the waveguide as low as 0.4 dB/cm was obtained at 1.31 μm. The propagation loss for transverse magnetic polarized light is 1.5 dB/cm. An ARROW waveguide fabricated using the polyimide-Ta₂O₅ -polyimide material system is also presented for comparison     

Effects of Si3N4, SiO, and polyimide surface passivations on GaAs MESFET amplifier RF stability

The effects of silicon nitride, silicon monoxide, and polyimide MESFET passivations on amplifier RF stability have been examined. GaAs MESFET amplifiers subjected to biased life tests show a time dependent "drift" in RF performance from turn on to hundreds of hours. These short- and long-term instabilities in performance have been correlated with surface effects. It was found that passivation with a surface dielectric such as Si3N4can eliminate this drift mechanism, while other dielectrics either delayed the onset of drift or had no desirable effects. Methods for deposition of these dielectrics and the relative merits of these methods are discussed.     

Reduction of base-collector capacitance in InP/InGaAs HBT's using anovel double polyimide planarization process

The parasitic base-collector capacitance (C_BC) in InP/InGaAs heterojunction bipolar transistors (HBTs) has been reduced using a novel double polyimide planarization process which avoids damage of the extrinsic base layer. The extrinsic base metal outside the base-collector mesa is placed on the polyimide by polyimide coating and etch-back to the base layer. We obtained f_T of 81 GHz and f _MAX of 103 GHz with a 2×10 μm emitter. Performance comparison between two devices with the same area of 2×2 μm but with different base-collector mesa area showed 56% reduction of C_BC and 35% increase of f_T and f_MAX     

Adhesion improvement of silicon/underfill/polyimide interfaces by UV/ozone treatment and sol–gel derived hybrid layers

Adhesion and mechanical reliability improvement is an important issue for flexible electronics due to weak bonds between silicon/underfill/polyimide interfaces. These interfaces are bonded with weak hydrogen and ester bonds which are vulnerable to humidity. Therefore, in this study, adhesion and reliability of silicon/underfill/polyimide interfaces are enhanced by using UV/Ozone treatment and sol–gel derived hybrid layers. In order to examine the effectiveness of those surface treatment methods, double cantilever beam (DCB) test and subcritical crack growth test were applied to accurately measure the adhesion energy and subcritical crack growth rate. The results showed that the adhesion and reliability against humidity were enhanced by more than 300% and 1000% when both surface treatment methods were applied. Also, the adhesive failure path was altered to mixed mode failure of both cohesive and adhesive failure paths.     

Electrical leakage at low-K polyimide/TEOS interface

The effect of low-K polymer passivation on electrical leakage was investigated to evaluate the reliability of polymer integration on device wafers. Polyimide passivation over Al(0.5% Cu) interconnects inlaid in TEOS increases the intralevel leakage current mainly along the polyimide/TEOS interface. Moisture absorbed in the polyimide further increases the inter facial as well as bulk leakages. These findings emphasize the importance of separating interconnects from direct contact with polyimide/TEOS interfaces to alleviate electrical isolation problems in multilevel interconnect architecture that employs low-K polymer dielectrics     

Light extraction enhancement in organic light-emitting diodes through polyimide/porous silica hybrid films

In this work, light extraction efficiency of organic light-emitting diodes (OLEDs) with a spin-coated polyimide/porous silica hybrids were enhanced. The polyimide/porous silica thin films (C1 and C2) were accomplished by spin coating a hybrid film composed of a polyimide-silica composite blended with various amount of porous silica nanoparticles into the opposite site of ITO glass. The optical, thermal, and morphology properties were controlled by adding various amount of porous silica. The incorporation of light extraction layer improved the maximum external quantum efficiency (EQE) by as much as 24.8% based on integrating sphere measurement condition when compared to that of a reference device without a light extraction layer. Furthermore, the device utilizing the light extraction layer showed identical EL spectra as the reference device did. Additionally, the optical emission distribution of the device was close to the Lambertian profile. The polyimide/porous silica hybrids demonstrated in this work are useful and efficient for OLED device for the enhancement of EL performance, indicating the potential in a wide range of applications, such as displays, lightings and so on.     

Compact ARROW-type vertical coupler filter

Compact wavelength filter utilizing the vertical coupling between a conventional ridge waveguide and a 3-D ARROW is proposed and demonstrated. Compact size and narrowband performance are achieved utilizing the large difference of waveguide dispersion between the 3-D ARROW and the ridge waveguide at single mode. A polyimide ridge waveguide was stacked on a stripe lateral confinement ARROW in an intersecting configuration with the interaction length of about 1 mm, and -3-dB linewidth of 5.5 nm was experimentally achieved.     

In situ measurement of mechanical properties of polyimide filmsusing micromachined resonant string structures

Two in situ measurement schemes, using micromachined resonant string structures, for the measurement of the polyimide residual stress and polyimide/metal adhesion durability have been developed. The residual stress of polyimide films, DuPont PI-2555 and PI-2611, have been measured using a bulk micromachined string structure. According to the Rayleigh's method, the resonant frequency of a polyimide string can be related to the film stress. By measuring the resonant frequency of these polyimide strings, the residual stresses have been calculated. The measurement results of various strings have been compared with conventional measurement results, which shows that they are in good agreement. Also, a noble scheme to quantize the adhesion durability between a polyimide film and a metal film has been developed. This scheme is based on a polyimide/metal bimorph string structures, fabricated using a surface micromachining technique, vibrating with an alternating potential. The change of resonance profile of this string structure can be related to the degradation of adhesion strength at the polyimide/metal interface. Various polyimide/gold string structures have been fabricated using a surface micromachining with Cu sacrificial layers, and the resonant qualities have been monitored. Notable changes of resonant Q-factor and resonant frequency, due to the degradation of adhesion between the metal and polyimide, have been observed after 10 ⁸ cycles (string vibration) for the polyimide/gold bimorph strings. The changes of resonant Q-factor and resonant frequency over a time period (vibration cycles) have been monitored     

Optical signal distribution to MSM photodetector arrays viaintegrated polyimide waveguides

The integration of metal-semiconductor-metal (MSM) photodetector arrays with polyimide ridge waveguides is demonstrated. MSM detectors were fabricated using transparent indium tin oxide (ITO) interdigitated electrodes on semi-insulating GaAs substrates. An optical buffer layer of SiO₂ was deposited and patterned, and then polyimide ridge waveguides were fabricated on top by spin coating and photolithography. The guides were multimode with widths from 10 to 50 μm. Light at 830 nm was coupled efficiently from the waveguides through gaps in the SiO ₂ buffer layer into the underlying detector structures. Absolute responsivities of the integrated MSM devices were around 0.5 A/W and the 3 dB bandwidths of 5-6 GHz were measured. Division of the input signal between sets of two and four detectors under a single waveguide has been achieved, highlighting the potential for the fabrication of integrated optoelectronic switches     

An ARROW optical wavelength filter: design and analysis

A novel ARROW (antiresonant reflecting optical waveguide)-based optical wavelength filter is proposed. The modal characteristics of the coupled ARROW structures is analyzed rigorously by the transverse resonance method. As an alternative configuration to the conventional directional coupler filter, the proposed device features large core size compatible with fiber and nearly periodic dependence of the coupling-length on the waveguide separation, which provides more flexibility for fabrication of the device. A design procedure for this type of coupled ARROW structure used for wavelength filtering is presented. The devices designed are simulated and verified by the beam propagation method. An ARROW wavelength filter based on SiO₂/TiO₂ has a FWHM bandwidth narrower than 7 Å     

A Low Phase-Noise X-Band MMIC VCO Using High-Linearity and Low-Noise Composite-Channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMTs

A low phase-noise X-band monolithic-microwave integrated-circuit voltage-controlled oscillator (VCO) based on a novel high-linearity and low-noise composite-channel Al_0.3Ga_0.7N/Al_0.05Ga_0.95 N/GaN high electron mobility transistor (HEMT) is presented. The HEMT has a 1 mumtimes100 mum gate. A planar inter-digitated metal-semiconductor-metal varactor is used to tune the VCO's frequency. The polyimide dielectric layer is inserted between a metal and GaN buffer to improve the Q factor of spiral inductors. The VCO exhibits a frequency tuning range from 9.11 to 9.55 GHz with the varactor's voltage from 4 to 6 V, an average output power of 3.3 dBm, and an average efficiency of 7% at a gate bias of -3 V and a drain bias of 5 V. The measured phase noise is -82 dBc/Hz and -110 dBc/Hz at offsets of 100 kHz and 1 MHz at a varactor's voltage (V_tune)=5 V. The phase noise is the lowest reported thus far in VCOs made of GaN-based HEMTs. In addition, the VCO also exhibits the minimum second harmonic suppression of 47 dBc. The chip size is 1.2times1.05 mm²     

Fabrication and adhesion strength of Cu/Ni-Cr/polyimide films for flexible printed circuits

The adhesion strength of a Cu/Ni-Cr/polyimide flexible copper clad laminate (FCCL), was evaluated according to the thickness of the Ni-Cr (Ni:Cr = 95:5 ratio) seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by SEM, AFM and XPS. The peel strength of the FCCL increased with increasing thickness of the Ni-Cr seed layer, due to the increase in the ion bombardment caused by the higher power used in the Ni-Cr sputtering process. This increase in the FCCL peel strength was attributed to the lower proportion of C-N bonds and higher proportion of C-O bonds in the polyimide surface. The adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.     

Loss reduction of an ARROW waveguide in shorter wavelength and itsstack configuration

The reduction of the propagation loss of an antiresonant reflecting optical waveguide (ARROW) to 0.3 dB/cm in a short-wavelength band by using transparent TiO₂/SiO₂ interference cladding is discussed. An analysis method for ARROW is developed to analyze its propagation characteristics. Two uncoupled parallel ARROWs were stacked with 2-μm spacing, to obtain three-dimensional optical interconnection     

Recombination current reduction in AlGaAs/GaAs heterojunction bipolar transistors with polyimide deposition

N-p-n AlGaAs/GaAs heterojunction bipolar transistors of various emitter-mesa diameters have been fabricated to examine the effects on the recombination current with polyimide deposition. The recombination current in these devices (when the ideality factor is close to 2) was proportional to the device perimeter before and after polyimide deposition. This suggests that the dominant component of the recombination current in these devices is the perimeter recombination current. A simple model was developed which allowed the contribution from the perimeter and bulk recombination currents to be calculated. The common-emitter d.c. current gains of these devices increased correspondingly as recombination current decreased due to the polyimide deposition.     

Some effects of anisotropy on planar antiresonant reflectingoptical waveguides

In this paper, propagation characteristics of some planar antiresonant reflecting optical waveguides (ARROW's) comprised of anisotropic media are studied using an integral equation approach. The integral equation method is rigorous and general, with the added advantage that multiple layers of crystalline material with arbitrary anisotropy can be accommodated in a straightforward manner. The integral equation method is applied to study basic propagation characteristics of the ARROW structure where one or more dielectric layers are allowed to be anisotropic. Practically, the presence of anisotropy may be unintentional, due to material fabrication or processing techniques, or it may be intentionally utilized to allow integration of anisotropy-based devices and waveguiding structures on a single semiconducting substrate. Propagation characteristics and field distributions are shown for a uniaxially anisotropic ARROW where the material's optic axis is rotated in each of the three principal geometrical planes of the structure. It Is found that even moderately large levels of anisotropy do not significantly affect the propagation characteristics of the ARROW if either the optic axis of the material is aligned with one of the geometrical axes of the waveguide, or if the optic axis is rotated in the equatorial plane. In these cases, pure TE ₀ modes can propagate, resulting in a low-loss structure. In the event of misalignment between the geometrical axes and the material's optic axis in the transverse or polar planes, the influeuce of even small levels of anisotropy is quite pronounced. In this case, pure TE₀ modes do not exist, and attenuation loss increases significantly due to the hybrid nature of the fundamental mode     

Reliability of InGaAs/InP long-wavelength p-i-n photodiodes passivated with polyimide thin film

The long-term reliability of InGaAs/InP p-i-n photodiodes passivated with polyimide thin film was studied through a room temperature life test and through thermally accelerated life tests. No degradation in dark current was observed in a room temperature life test at a reverse bias of -15 V after aging for 7000 h. However, the dark current increased gradually in the accelerated life tests at 110°C, 130°C, and 150°C. It was confirmed that the activation energy of degradation in dark current was 0.85 eV and the average lifetime was estimated to be 10⁷h at room temperature. The dark current recovered in high temperature storage tests. The phenomenon of degradation and recovery was qualitatively explained by a model of accumulation and diffusion of mobile ions at a junction perimeter.     

BCB/SiO_2双导芯层叠ARROW结构压力传感器设计

针对传统ARROW压力传感器耦合长度长以及耦合效率低,提出了BCB/SiO2双导芯层叠ARROW结构压力传感器。在外力作用下,弹性薄膜上的BCB/SiO2双导芯层叠ARROW结构,会因光弹效应致使BCB和SiO2两个导芯折射率变化产生输出相位差。通过有限元方法(FEM)研究硅弹性薄膜上导芯折射率的变化与应力分布关系,确定传感器的结构设计参数。使用束传播法(BPM)分析耦合结构以及压力与输出之间的关系。结果表明,该传感器无需弯曲波导即可降低器件尺寸,并实现了灵敏度为5.2×10-2/kPa压力检测。     

Bistabilities of Birefringent Vertical-Cavity Semiconductor Optical Amplifiers With Antiresonant Reflecting Optical Waveguide

Bistable characteristics of birefringent antiresonant reflecting-optical-waveguide (ARROW) vertical-cavity semiconductor optical amplifiers (VCSOA) under external optical injection with multi-mode profile and arbitrary polarization orientation are investigated theoretically. It is found that the presence of ARROW can realize stable single-mode bistable switching in VCSOAs. Furthermore, with suitable design of the bias current profile, it can be shown that ARROW VCSOAs with a large core diameter (i.e., ${ge 50}~mu{hbox {m}}$) can sustain stable single-mode bistable switching.      

The application of polyimide/silicon nitride dual passivation to AlxGa1−xN/GaN high electron mobility transistors

PECVD silicon nitride passivation is quite frequently done at the end of AlGaN/GaN HEMT fabrication before substrate back-side lapping. However, the PECVD silicon nitride process is likely to produce pinholes in the passivation film. A very thick PECVD silicon nitride film may produce mechanical stress on the underlying device. Polyimide passivation has also been known to be effective for AlGaN/GaN HEMT and it can also serve as a stress buffer. However, polyimide can take up water while PECVD silicon nitride is a good diffusion barrier for water, etc. Thus it is expected that a dual PECVD silicon nitride/polyimide passivation will be a better choice than just a single layer of PECVD silicon nitride or polyimide. In this paper, we will demonstrate the application of a dual PECVD silicon nitride/polyimide passivation to AlGaN/GaN HEMT process.