Benzocyclobutene Polymer Research Articles

Multimode interference wavelength multi/demultiplexer for 1310 and 1550 nm operation based on BCB 4024-40 photodefinable polymer

A 1310 and 1550 nm coarse wavelength multi/demultiplexer based on benzocyclobutene (BCB 4024-40) polymer is demonstrated for the first time. The device is designed based on a combination of general interference and paired interference mechanisms of multimode interference (MMI). It is fabricated on BK7 glass substrate with a thin layer of SiO 2 as cover. A cost effective chemical etching technique is used in the fabrication process to take advantage of the photosensitive nature of the polymer. The device length was significantly reduced by adopting the restricted multimode interference scheme, lower beat length ratio and cascaded MMI couplers. The measured crosstalk at 1310 nm was 14.4 dB and at 1550 nm was 20.6 dB. The measured insertion loss is around 3.2–3.5 dB for both ports.

Multimode interference optical splitter based on photodefinable benzocyclobutene (BCB 4024-40) polymer

1×2 and 1×3 planar optical splitters based on Benzocyclobutene (BCB 4024-40) polymeric material are demonstrated for the first time. The devices are designed based on symmetric interference and fabricated on BK7 glass substrates with a thin layer of SiO2 as cover. A cost-effective chemical etching technique is used in the fabrication process to take advantage of the photosensitivity of the polymer. The waveguide loss was measured using the cutback method to be 3.5 dB/cm. The splitting uniformity is better than 0.02 and 1.5 dB at 1550-nm optical wavelength for the 1×2 and 1×3 splitters, respectively.

Reduced Temperature Dependence of Lasing Wavelength in Membrane Buried Heterostructure DFB Lasers With Polymer Cladding Layers

An athermal operation of the lasing wavelength in a membrane buried heterostructure distributed feedback (BH-DFB) laser was demonstrated by adopting a polymer (benzocyclobutene) cladding layer which has a negative temperature coefficient of refractive index. Membrane BH-DFB lasers of core thickness 65 nm were operated under room-temperature continuous-wave conditions. The temperature dependence of the lasing wavelength was measured to be 2.45times10-2 nm/degC, which is about 20%-30% of that for conventional semiconductor lasers

Single mode optical waveguides based on photodefinable benzocyclobutene (BCB 4024–40) polymer

AbstractThe fabrication and characterization process of BenzoCyclobutene (BCB 4024–40) polymer waveguides are described. The polymer film thickness for various coating speed and refractive index are measured by the method of prism coupling. A cost effective chemical etching technique is used in the waveguide fabrication process to take advantage of the photosensitive nature of the polymer. The waveguide loss is measured using the conventional cut back method which results on an average loss of 3.5 dB/cm. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 479–481, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22150

Modeling and optimization of a fast response capacitive humidity sensor

This paper presents a model which predicts the temporal response of capacitive humidity sensors made of parallel electrodes and a polymer sensitive coating. This model is used for the simulation of the response of the sensor subjected to specific conditions. The model includes electrostatic and molecular diffusion calculation. As a validation, the model is confronted with finite-element simulation and experimental results. Experiments were carried out for divinyl siloxane benzocyclobutene (DVS-BCB) polymer films with different film thicknesses and upper electrode dimensions. As an application example, the model is used to simulate the response of several humidity sensor structures exposed to the conditions of a medical application related to breath analysis. The model may also be helpful to predict the effects of fabrication process uncertainties. Because the model used to describe water diffusion in DVS-BCB is based on Henry's law and Fick's law, it could be extended to the optimization of capacitive sensors for other vapors

Biosensors for label free detection based on RF and MEMS technology

A bio-detection method and devices based on RF electric signals and MEMS are proposed and demonstrated by a label free method. We have fabricated a transmission line, an inductive device, and a capacitive device with silicon-based MEMS technology. Main issues are fabrication of devices by MEMS technology, surface modification from hydrophobic to hydrophilic of a benzocyclobutene (BCB) layer by plasma radiation and RF signal measurement before and after bio-processing. The devices made by MEMS technology consist of a BCB polymer and Cu metal patterns on a silicon substrate. Glucose oxidase (GOx) and poly dimethyldiallyl ammonium chloride (PDAC) are used as a biomolecule target and probe. The measured output of power loss is 0.8 dB at 1.9 GHz, and its value is pretty distinguishable from the noise level. From the above-mentioned results, it is clear that the proposed RF method and designs are very effective and powerful as a label free detection system.

Biocompatible benzocyclobutene-based intracortical neural implant with surface modification

This paper presents the fabrication of a benzocyclobutene (BCB) polymer-based intracortical neural implant for reliable and stable long-term implant function. BCB polymer has many attractive features for chronic implant application: flexibility, biocompatibility, low moisture uptake, low dielectric constant and easy surface modification. A 2 µm thick silicon backbone layer was attached underneath a flexible BCB electrode to improve mechanical stiffness. No insertion trauma was observed during penetrating into the dura of a rat. In vitro cytotoxicity tests of the completed BCB electrode revealed no toxic effects on cultured cells. The modified BCB surface with a dextran coating showed a significant reduction in 3T3 cell adhesion and spreading, indicating that this coating has the potential for lowering protein adsorption, minimizing inflammatory cell adhesion and glial scar formation in vivo, and thereby enhancing long-term implant performance.

Embedded benzocyclobutene in silicon: An integrated fabrication process for electrical and thermal isolation in MEMS

This paper reports a novel fabrication process to develop planarized isolated islands of benzocyclobutene (BCB) polymer embedded in a silicon substrate. Embedded BCB in silicon (EBiS) can be used as an alternative to silicon dioxide in fabrication of electrostatic micromotors, microgenerators, and other microelectromechanical devices. EBiS takes advantage of the low dielectric constant and thermal conductivity of BCB polymers to develop electrical and thermal isolation integrated in silicon. The process involves conventional microfabrication techniques such as photolithography, deep reactive ion etching, and chemical mechanical planarization (CMP). We have characterized CMP of BCB polymers in detail since CMP is a key step in EBiS process. Atomic force microscopy (AFM) and elipsometry of blanket BCB films before and after CMP show that higher polishing down force pressure and speed lead to higher removal rate at the expense of higher surface roughness, non-uniformity, and scratch density. This is expected since BCB is a softer material compared to inorganic films such as silicon dioxide. We have observed that as the cure temperature of BCB increases beyond 200 °C, the CMP removal rate decreases drastically. The results from optical microscopy, scanning electron microscopy, and optical profilometry show excellent planarized surfaces on the EBiS islands. An average step height reduction of more than 95% was achieved after two BCB deposition and three CMP steps.

Self-Aligning Planarization and Passivation for Integration Applications in III–V Semiconductor Devices

This work reports an easy planarization and passivation approach for the integration of III-V semiconductor devices. Vertically etched III-V semiconductor devices typically require sidewall passivation to suppress leakage currents and planarization of the passivation material for metal interconnection and device integration. It is, however, challenging to planarize all devices at once. This technique offers wafer-scale passivation and planarization that is automatically leveled to the device top in the 1-3-/spl mu/m vicinity surrounding each device. In this method, a dielectric hard mask is used to define the device area. An undercut structure is intentionally created below the hard mask, which is retained during the subsequent polymer spinning and anisotropic polymer etch back. The spin-on polymer that fills in the undercut seals the sidewalls for all the devices across the wafer. After the polymer etch back, the dielectric mask is removed leaving the polymer surrounding each device level with its device top to atomic scale flatness. This integration method is robust and is insensitive to spin-on polymer thickness, polymer etch nonuniformity, and device height difference. It prevents the polymer under the hard mask from etch-induced damage and creates a polymer-free device surface for metallization upon removal of the dielectric mask. We applied this integration technique in fabricating an InP-based photonic switch that consists of a mesa photodiode and a quantum-well waveguide modulator using benzocyclobutene (BCB) polymer. We demonstrated functional integrated photonic switches with high process yield of >90%, high breakdown voltage of >25 V, and low ohmic contact resistance of /spl sim/10 /spl Omega/. To the best of our knowledge, such an integration of a surface-normal photodiode and a lumped electroabsorption modulator with the use of BCB is the first to be implemented on a single substrate.

Thermal parameters identification of micrometric layers of microelectronic devices by thermoreflectance microscopy

The objective of this paper is the determination of the thermal properties of micrometric layers of electronic devices using a thermoreflectance probe. Unlike classical thermoreflectance methods, the main point of the method presented in this paper is to be able to quantify the heating energy (by Joule effect) and the effective temperature response (by calibration). It is then possible to estimate the thermal conductivity (in Wm−1K−1) instead of the thermal diffusivity (in m2s−1). A semi-analytical thermal 3D-periodic model then enables to identify a few thermal properties of the layers of the device, and in particular the thermal conductivity of the passivation layer. This methodology has been applied to the study of an industrial device containing interconnect test structures made of copper lines on a silicon wafer with a few micrometers BCB (BenzoCycloButene) polymer passivation layer. The BCB thermal conductivity and the metal heat capacity are obtained using this method.

Characterization of benzocyclobutene optical waveguides fabricated by electron‐beam direct writing

AbstractOptical waveguides based on benzocyclobutene polymer are fabricated by electron‐beam direct writing without etching. The propagation losses of waveguide measured at 1.55 μm for both TE and TM polarizations are 0.76 and 0.86 dB/cm, respectively. Moreover, the characteristics of waveguide bends are discussed for comparison. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 208–210, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20254

Polyamide-imide polymer thin films for integrated optics

The applicability of a polyamide-imide (PAI) polymer to thin film optical applications was investigated. The polymer preparation and spin characteristics are described in detail. The films exhibited good adhesion to silicon, glass, and benzocyclobutene polymer. The refractive index was measured in the near infrared region. To demonstrate feasibility for devices, features were plasma etched into PAI films. Oversized inverted rib waveguides were also fabricated using PAI as a core material, and losses as low as 0.2 dB/cm were measured at 830 nm. Polyamide-imide is a highly robust and stable polymer, similar to the widely used polyimides, and is an excellent candidate material for integrated optics applications.

Polyamide-imide polymer thin films for integrated optics

The applicability of a polyamide-imide (PAI) polymer to thin film optical applications was investigated. The polymer preparation and spin characteristics are described in detail. The films exhibited good adhesion to silicon, glass, and benzocyclobutene polymer. The refractive index was measured in the near infrared region. To demonstrate feasibility for devices, features were plasma etched into PAI films. Oversized inverted rib waveguides were also fabricated using PAI as a core material, and losses as low as 0.2 dB/cm were measured at 830 nm. Polyamide-imide is a highly robust and stable polymer, similar to the widely used polyimides, and is an excellent candidate material for integrated optics applications.

Birefringence characteristics of benzocyclobutene rib optical waveguides

Zero-birefringence benzocyclobutene polymer rib waveguides as well as waveguides that exhibit low birefringence over a wide range of temperature are demonstrated. Experimental results agree well with theoretical calculations that take into account stress-induced birefringence.

Optical interconnections on electrical boards using embedded active optoelectronic components

Significant opportunities are emerging for optical interconnections at the board, module, and chip level if compact, low loss, high data rate optical interconnections can be integrated into these electrical interconnection systems. This paper describes an integration process for creating optical interconnections which can be integrated in a postprocessing format onto standard boards, modules, and integrated circuits. These optical interconnections utilize active thin-film optoelectronic components embedded in waveguides, which are integrated onto or into the interconnection substrate, thus providing an electrical output on the substrate from an optical interconnection. These embedded optical interconnections are reported herein using BCB (Benzocyclobutene ) polymer optical waveguides in two different formats, as well as a third waveguide structure using a BCB cladding with an Ultem core. All of these waveguides were fabricated with InGaAs-based thin-film inverted metal-semiconductor-metal (I-MSM) photodetectors embedded in the waveguide layer, thus eliminating the need for beam turning elements at the output of the waveguide. These embedded interconnections have been fabricated and tested, and the coupling efficiency of the optical signals from the waveguides to the embedded photodetectors was estimated from these measurements. These measurement-based estimates are then compared to theoretical models of the coupling efficiency. Using the theoretical coupling efficiency model, variable coupling can be engineered into the interconnect design, thus enabling partial coupling for arrays of photodetectors embedded in waveguide interconnections.

GaInAsP Microdisk Injection Laser with Benzocyclobutene Polymer Cladding and Its Athermal Effect

We fabricated a GaInAsP microdisk laser using a benzocyclobutene (BCB) polymer cladding, which decreased the fragility and the thermal resistance of the conventional air cladding device and simplified the current injection using the metal pad electrode. The threshold current for a 7-µm-diameter device was 0.4 mA at room temperature, which was almost the same as that for the air cladding device. The red shift of the resonant spectrum against the continuous wave current was reduced by 54% in the BCB cladding device. Nearly 90% of this reduction is attributed to the reduction in thermal resistance. The remaining 10% is due to the reduction in temperature dependence (athermal effect) by the BCB cladding which has a negative temperature dependence of the refractive index. An analysis shows that the microdisk laser with a polymer cladding can function as an athermal laser when the disk thickness is reduced to 50–80 nm.

Overview of Photo-definable Benzocyclobutene Polymer.

Benzocyclobutene (BCB) polymer was developed at Dow Chemical in the late 1980's for microelectronics packaging and interconnect applications. Photo-definable BCB formulation was commercialized in 1994. The Dielectric polymer films produced from BCB formulations possess many desirable properties[1] [2] [3] [4] for microelectronic applications; for example, low dielectric constant and dissipation factor, low moisture absorption, rapid curing and low temperature cure without generating by-products, minimum shrinkage in curing process, and no Cu migration issues. Derived from these properties, applications have been developed in: bumping/wafer level packaging [5][6], Ga/As chip ILD [7], optical wave guide [8], flat panel display [9], and lately in BCB-coated Cu foil for build-up board [10]. This article summaries the chemistry, the relevant properties and the typical process of photo definable divinylsiloxane bisbenzocyclobutene (DVS-BCB) commercialized by Dow Chemical as CYCLOTENETM resin system.

Hybrid Integration of III-V Optoelectronic Devices on Si Platform Using BCB

ABSTRACTIntegration of dense arrays of high frequency III-V photoemitters and photodetectors with Si platform is one of the challenging tasks for realization of novel chip-level optical interconnects. These interconnects require the resolution of numerous problems of compatibility of materials. Comparison of monolithic and hybrid integration technologies highlights the advantages of hybrid approaches for emitters highly sensitive to growth defects. A novel protocol for fabrication of III-V optoelectronic components on a Si platform is proposed. Reversed vertical cavity surface emitting laser (VCSEL) structures were grown homoepitaxialy by MBE on a GaAs substrate, and then bonded to a Si wafer using a benzocyclobutene (BCB) polymer. The GaAs substrate was subsequently removed by selective etching down to an AlAs etch stop layer. This reduces thermal stresses in order to enhance the optoelectronic device performance and increase lifetime. A 10 μm-thick high frequency VCSEL with coplanar metallization is processed on Si with PMGI reflow planarization. Electro-luminescence spectrum, I-V and P-T characteristics were measured and compared with a reference structure. It was found that measured thermal resistance is about five times higher than for devices on a host GaAs wafer.

Deeply Etched Semiconductor/Benzocyclobutene Distributed Bragg Reflector Laser Combined with Multiple Cavities for 1.5-µm-Wavelength Single-Mode Operation

Single-mode GaInAsP lasers at a wavelength of 1.5 µm, fabricated using deep dry-etching technology are presented. In the novel design, the high reflectivity of a fifteen-element distributed Bragg reflector (DBR) is combined with the spectral selectivity of multiple cavities (MC) to achieve single-mode operation with high output efficiency. The etched structure was buried with polymer benzocyclobutene (BCB) in order to reduce the diffraction loss between coupled cavities, to passivate the sidewalls of the waveguide and to protect the structure from damage due to process handling. MC lasers with different numbers of cavities were analyzed by the transfer matrix method (TMM) including groove losses and the results of analysis are compared with experimental results of fabricated devices. For a coupled cavity (CC) laser, which has only two cavities, a threshold current of 11 mA and a submode suppression ratio (SMSR) of 36 dB at a bias current of 1.8 times the threshold were obtained for 5-µm-wide mesa stripe geometry.

Polymer photonic crystal slab waveguides

We present details of the fabrication, calculations, and transmission measurements for finite two-dimensional (2D) polymer photonic crystal (PC) slab waveguides, which were fabricated from a benzocyclobutene polymer on a low refractive index substrate from Teflon. A square air hole lattice (500 nm lattice constant, 300 nm hole diameter) was realized by electron beam lithography and reactive ion etching. Polarization and wavelength dependent transmission results show TE-like and TM-like stop gaps at 1.3 μm excitation wavelengths and are in good agreement with the calculated data obtained by 2D and three-dimensional finite difference time domain methods. Transmission was suppressed by 15 dB in the center of the TE-like stop gap for a PC length of ten lattice constants.