Terabus: Terabit/Second-Class Card-Level Optical Interconnect Technologies

In the “Terabus” optical interconnect program, optical data bus technologies are developed that will support terabit/second chip-to-chip data transfers over organic cards within high-performance servers, switch routers, and other intensive computing systems. A complete technology set is developed for this purpose, based on a chip-like optoelectronic packaging structure (Optochip), assembled directly onto an organic card (Optocard). Vertical-cavity surface emitting laser (VCSEL) and photodiode arrays (4$,times,$12) are flip-chip bonded to the driver and receiver IC arrays implemented in 0.13-$mu$m CMOS. The IC arrays are in turn flip-chip assembled onto a 1.2-cm$^2$silicon carrier interposer to complete the transmitter and receiver Optochips. The organic Optocard incorporates 48 parallel multimode optical waveguides on a 62.5-$mu$m pitch. A simple scheme for optical coupling between the Optochip and the Optocard is developed, based on a single-lens array etched onto the backside of the optoelectronic arrays and on 45$^circ$mirrors in the waveguides. Transmitter and receiver operation is demonstrated up to 20 and 14 Gb/s per channel, respectively. The power dissipation of 10-Gb/s single-channel links over multimode fiber is as low as 50 mW.     

Hybrid integration of VCSEL's to CMOS integrated circuits

Three hybrid integration techniques for bonding vertical-cavity surface-emitting lasers (VCSELs) to CMOS integrated circuit chips have been developed and compared in order to determine the optimum method of fabricating VCSEL based smart pixels for optical interconnects and free-space optical processing. Each of the three bonding techniques used different ways of attaching the VCSEL to the integrated circuit and making electrical contacts to the n- and p-mirrors. All three techniques remove the substrate from the VCSEL wafer leaving an array of individual VCSELs bonded to individual pixels. The 4×4 and/or 8×8 arrays of bonded VCSELs produced electrical and optical characteristics typical of unbonded VCSELs. Threshold voltages down to 1.5 V and dynamic resistance as low as 30 Ω were measured, indicating good electrical contact was obtained. Optical power as high as ~10 mW for a VCSEL with a 20-μm aperture and 0.7 mW with a 6-μm aperture were observed. The VCSELs were operated at 200 Mb/s (our equipment limit) with the rise and fall times of the optical output <1 nS     

Design and fabrication of VCSELs withAlxOy-GaAs DBRs

A procedure for fabricating vertical-cavity surface-emitting lasers (VCSELs) with oxide-based distributed Bragg reflectors (DBRs) is presented. An in-depth analysis of parameters and behavior unique to oxide VCSELs determines the device design. The development cycle time for these devices is reduced through development of a method for post-growth analysis of the epitaxial stack reflectivity before device processing. Threshold currents as low as 160 μA and resistances as low as 80 Ω are demonstrated using different device designs. The total optical loss of low-doped oxide VCSEL structures is 0.163% which is comparable to VCSEL designs based on all-semiconductor DBRs. The thermal resistance of an 8×8 μm VCSEL is measured to be 2.8°C/mW, demonstrating that the presence of oxide layers does not act as a barrier to heat flow out of the active region     

1.3-$mu$m Four-Channel$,times,$10-Gb/s Parallel Optical Transceiver With Polymer PLC Platforms for Very-Short-Reach Applications

A four-channel$times10$-Gb/s parallel optical transceiver for high-capacity very-short-reach applications was developed. The transceiver module was fabricated with low-cost components such as polymer planar lightwave circuit (PLC) platforms and 1.3-$mu$m Fabry–Perot laser diodes (FPLDs). The polymer PLC platform enables the FPLDs or waveguide photodiodes (WGPDs) to be butt-coupled to the polymer waveguide by low-cost passive alignment. Using 1.3-$mu$m FPLDs and single-mode fibers (SMFs) achieves reliable transmission over 600 m. Widening the spacing between the waveguides up to 1 mm suppressed the interchannel crosstalk to below$-39$dB. The fabricated transceiver was operated at 10 Gb/s per channel and it successfully demonstrated 600-m error-free transmission. The sensitivity of each channel was better than$-14$dBm with an interchannel-crosstalk penalty of less than 0.7 dB.     

All-optical inverter based on long-wavelength vertical-cavity surface-emitting laser

An all-optical inverter using transverse mode switching in a 1.5-/spl mu/m vertical-cavity surface-emitting laser (VCSEL) was demonstrated theoretically and experimentally. The fundamental mode in a single-mode VCSEL was strongly suppressed when external light was injected into an LP02 high-order mode, resulting in an on-off ratio of over 20 dB. The polarization dependence of the static optical input--output characteristics of inverter operations was as low as /spl sim/13%. The VCSEL-based optical inverter operated with a 5-Gb/s nonreturn-to-zero (NRZ) input signal. A theoretical result using two-mode rate equations is in good agreement with experimental results.     

Fundamental characteristics of a MEMS‐diaphragm actuator using a thermal expansion drive composed of a conductive polymer

Performance of a MEMS actuator using a thermal expansion drive of a conductive polymer (CP) is investigated by applying electricity to it. The actuator consists of a thin polymer diaphragm (5 mm diameter) and a thin CP (ion‐doped polythiophene) layer coated on the diaphragm surface. Polyimide (10 μm thickness) and PET (110 μm thickness) sheets were chosen as the diaphragm materials. The diaphragm is deflected by the thermal expansion of the CP by applying electricity to it. Merits of using the CP instead of metal are realizing flexible actuators and the applicability to a low‐heat‐resistant material diaphragm. The relationship between thickness of the CP layer (10–50 μm thickness) and electrical resistance (30–600 Ω) and the relationship between the input voltage (1–8 V) and the generated diaphragm displacement (several tens of micrometers) were investigated experimentally. These relationships were compared with those in the case of using the thermal expansion of a vapor‐deposited aluminum layer (0.1 μm thickness). The results of the investigation indicate that the diaphragm based on CP can produce the required displacement. In the case the CP‐layer‐based thermal expansion, however, larger input voltage than in the case of the aluminum‐layer‐based thermal expansion is needed to obtain the same displacement amplitudes. Therefore, the main problem concerning use of the CP‐based diaphragm is considered to be enhancing the electrical conductance of the CP layer. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Effects of device design on InP-based HBT thermalresistance

The thermal resistance of InP-based single and double heterojunction bipolar transistors has been measured. The double heterojunction bipolar transistor (DHBT) device employs an InP collector to improve thermal conductivity and reduce the base-emitter junction temperature rise. DHBTs were grown with heavily doped InGaAs or InP sub-collectors for low resistance contacts. As expected, the all-InP collector (sub-collector and collector) had the lowest thermal resistance while the all-InGaAs collector (sub-collector and collector) had the highest thermal resistance. For a device with emitter size of 1 × 3 μm², the room temperature thermal resistance of the all-InP collector DHBT was 3.9°C/mW. The DHBT with an InGaAs sub-collector had a thermal resistance of 5.6°C/mW, while the SHBT had a thermal resistance of 12.3°C/mW. Also compared were effects of device layout parameters on thermal resistance and the effect of the topside metal thickness. Devices with the largest perimeter-to-area ratio had the lowest thermal resistance when normalized to emitter area. HBTs with conservative alignment tolerances (L1) had similar thermal resistance to those with aggressive alignment tolerances (L2). The reduced parasitic capacitance of the L2-style SHBT improved the device f _T from 150 to 183 GHz at 6.0-mA collector current. Alternately, the reduced parasitics allowed the SHBT to operate at 150 GHz f_T at 2.9 mA, reducing the junction temperature rise by more than half. Doubling the topside metal thickness improved the thermal resistance by 31% at room temperature     

Growth of highly strained GaInAs-GaAs quantum wells on patterned substrate and its application for multiple-wavelength vertical-cavity surface-emitting laser array

We carried out the growth of highly strained GaInAs-GaAs quantum wells (QWs) on a patterned substrate for extending emission wavelength on a GaAs substrate. We examined the shift of photoluminescence wavelength of the QWs and showed a large wavelength shift due to the spatial modulation in well thickness and indium composition. We demonstrated a single-mode multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) array on a patterned GaAs substrate covering a new wavelength window of 1.1-1.2 /spl mu/m. By optimizing pattern shape, we achieved multiple-wavelength operation with widely and precisely controlled lasing wavelengths. The maximum lasing span is as large as 77 nm. We carried out a data transmission experiment through 5-km of single-mode fiber with a 2.5 Gb/s/channel. The total throughput reaches 10 Gb/s. The VCSEL-based wavelength-division-multiplexing (WDM) source would be a good candidate for WDM-LAN beyond 10 Gb/s.     

Formation of ceramic thin films using electrospray in cone-jet mode

An electrostatic atomization technique has been developed to generate ultrafine spray droplets of ZrO₂ and SiC ceramic suspensions in a range of a few micrometers with a narrow size distribution. The aim of this paper is to deposit uniform thin films (from a few micrometers to a few tens of micrometers) of these ceramic materials on alloy substrates. Compared to some other thin-film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and plasma spray (PS), etc., the thin-film deposition process using electrostatic atomization is not only cheap but also capable of depositing a very thin multilayer with abrupt interfaces. CVD and PVD are expensive techniques. They require either a high vacuum, even an ultrahigh vacuum environment or complex gas handling system. Their deposition rate is also low. PS is normally used to grow thermal barrier coatings which usually have a thickness of a few tens to a few hundreds micrometers. Its application is limited by the quality of the coatings (high porosity, coarse and nonuniform microstructure). Preliminary results in this work have shown that, for low through-put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution, which is crucial to produce uniform thin films. It was found that the size of ceramic particles in ZrO₂ and SiC thin films is less than 10 μm. Microstructures of these thin films show very homogenous morphologies. These results indicate that ceramic thin films with high homogeneity can be deposited using electrostatic atomization. It was also observed that the morphology of the underlayer has some influence on the morphology of the top layer     

Modeling of noise and distortion associated with ultra‐high‐speed modulation of VCSEL with slow‐light feedback

This paper presents numerical modeling on the noise properties and signal distortion associated with millimeter‐frequency modulation of vertical‐cavity surface‐emitting laser (VCSEL) under with a transverse‐coupled cavity. The study is based on a time‐delay rate equation model that takes into account the multiple round trips in the feedback cavity and the optical loss and phase delay in each round trip. Strong slow‐light feedback is found to boost the modulation bandwidth to frequencies approaching 70 GHz and induce resonance modulation due to photon–photon resonance (PPR) over passbands centered on frequencies reaching 90 GHz. We show that the relative intensity noise of the VCSEL with resonance modulation is enhanced when the noise frequency approaches the corresponding PPR frequency VCSEL. The same effect applies for the VCSEL with extended carrier‐photon resonance (CPR) at the CPR frequency. The low‐frequency part is characterized by flat (white) noise of level nearly equal to −140 dB/Hz. The second‐harmonic distortion (2HD) values are smaller than −10 dB under small‐signal modulation and increase to lower than −5 dB when the modulation index becomes 0.3. Copyright © 2015 John Wiley & Sons, Ltd.     

An effective device design for thermal management of multifinger InGaP/GaAs collector‐up HBTs

An effective device structure for thermal management of multifinger InGaP/GaAs collector‐up heterojunction bipolar transistors (HBTs), compelling active components in high‐efficiency handset power amplifiers, is presented for the first time. From the unique 3‐D thickness‐adjusting numerical analysis, based on a finite element model, the miniaturized device can lead to a greater than 40% reduction in the thickness of plated gold layer. Above all, this is quite different from previous attempts, in which the thermal resistance was reduced by increasing the thickness of plated gold layer. Compared with literature works, the thermally stable design with an innovative heat‐spread configuration shows a 50% reduction in thermal resistance and demonstrates favorable power performance. Copyright © 2013 John Wiley & Sons, Ltd.     

Sixth-order differential Sallen-and-Key switched capacitor LPF using a-IGZO TFTs

This paper presents sixth-order fully differential active low pass RC and switched-capacitor (SC) filters using N-type IGZO thin-film transistors for flexible wearable continuous health monitoring systems. As a first step, a low-gain amplifier using a diode-connected load and a fully differential amplifier is designed with positive feedback based on capacitor bootstrapping. These amplifiers present a gain around 5.03 and 40 dB, respectively, whereas their respective GBW product are around 450 and 200 kHz. Then these amplifiers are employed to realize biquads, with which a sixth-order Sallen-Key low-pass RC and SC filters are implemented. The SC filter realized with low-gain DDA has shown a simulated THD of −30.9 dB, SFDR of 30.1 dB, and a power consumption of 456 μW. On the other hand, the SC filter presents a THD of −31.4 dB, SFDR of 32.2 dB, and a power consumption of 573 μW with high-gain differential difference amplifier (DDA) when a power supply of 10 V is used. Circuit simulations have been carried out in Cadence Virtuoso using in-house IGZO TFT models.     

Design and Performance of a Room-Temperature Terahertz Detection Array for Real-Time Imaging

A simple mass producible detection array for terahertz radiation has been designed and fabricated. The 1 mm times 1 mm pixels consist of a 0.5 mm times 0.5 mm thin-film absorber on a membrane, supported by 0.28-mm-wide silicon separation beams. Thermopiles are used to measure the temperature increase of the absorber. The 5 ms thermal time constant of the detector, together with the noise equivalent power of 1 nW/Hz^1/2, enables real-time imaging at 50 frames/s with a signal-to-noise ratio of 10 for an optical intensity of 30 muW/cm².     

温度传感器的应用技术

热电阻、热电偶是工业上常用的测温元件,是实现温度检测和控制的重要器件.温度传感器应用广泛、是发展最快的传感器之一.热电阻常用的有铂电阻和铜电阻,铂热电阻测温范围为-200～960℃;铜热电阻常用来做-50～+ 150℃范围内的工业用电阻温度计;热电偶测温范围下限达-270℃,上限达1800℃.     

Average optical power monitoring in micromirrors

The thermal properties of tip-tilt micromirrors have been analyzed theoretically and measured experimentally for devices operated in air and in vacuum. Typical micromirror thermal conductances are shown to range from 10^-3 W/K for devices operated close to the substrate in air to 10^-5 W/K for devices operated in a vacuum. These results demonstrate that micromirror temperatures are extremely sensitive to the average optical signal incident upon them and can be used as probes of incident power in much the same way as thermal infrared detectors. This has been experimentally demonstrated using a λ = 661 nm diode laser with polysilicon micromirrors, and sensitivities reaching below 70 nW of absorbed optical power, limited by the Johnson and 1/f noise of the micromirrors and measurement system. Average optical power monitoring could be useful in large cross connects or other applications, where the additional integration of a tap/beamsplitter plus photodiode assembly is undesirable     

Time evolution of laser-induced pyroelectric responses in aVDF/TrFE copolymer

Pyroelectric charge response induced by instantaneous heating using YAG laser pulse (7 ns) irradiation has been measured over a 1 ns to 10 s time range for a VDF/TrFE copolymer with composition 75/25 mol%. The observed spectra exhibited two damped oscillations associated with thermal expansion in the thickness and length directions coupled with piezoelectric effects. Removing these two components revealed pyroelectric responses consisting of an instantaneous component followed by a gradually increasing component. The instantaneous component appearing in parallel with the integrated laser intensity was attributed to primary pyroelectricity whose response time was <1 ns. The gradual component with time constant 200 ns was attributed to the relaxational nature of molecules and heat transfer from the electrode     

Investigation of 1.3-/spl mu/m GaInNAs vertical-cavity surface-emitting lasers (VCSELs) using temperature, high-pressure, and modeling techniques

We have investigated the temperature and pressure dependence of the threshold current (I/sub th/) of 1.3 /spl mu/m emitting GaInNAs vertical-cavity surface-emitting lasers (VCSELs) and the equivalent edge-emitting laser (EEL) devices employing the same active region. Our measurements show that the VCSEL devices have the peak of the gain spectrum on the high-energy side of the cavity mode energy and hence operate over a wide temperature range. They show particularly promising I/sub th/ temperature insensitivity in the 250-350 K range. We have then used a theoretical model based on a 10-band k.P Hamiltonian and experimentally determined recombination coefficients from EELs to calculate the pressure and temperature dependency of I/sub th/. The results show good agreement between the model and the experimental data, supporting both the validity of the model and the recombination rate parameters. We also show that for both device types, the super-exponential temperature dependency of I/sub th/ at 350 K and above is due largely to Auger recombination.     

Tracking and erosion of HTV silicone rubbers of different thickness

Tracking and erosion behaviors of high temperature vulcanized (HTV)-silicone rubber (SIR) of 0.5 to 6.0 mm thicknesses were investigated in order to obtain the optimum thickness for enhancing tracking and erosion resistance under various leakage current levels. Under low leakage current, thinner samples showed a higher tracking and erosion resistance, while under medium and high leakage current, thicker samples showed better resistance to these behaviors. The optimum thickness to prolong the time to tracking and erosion failure appeared in the range of 1.0 to 3.0 mm thickness. The content of an initial low molecular weight (LMW) silicone fluid was shown to be closely related to the development of leakage current and high temperature thermal spots. The results indicate that the sample thickness is crucial to the ability of HTV-SIR to withstand a large number of high temperature thermal spots under condition of high level leakage current     

Impacts of thermal aging and water absorption on the surfaceelectrical and chemical properties of cycloaliphatic epoxy resin

New techniques for measuring surface degradation are applied to the study of surface tracking resistance of materials intended for outdoor use. Cycloaliphatic epoxy resin (CAE) with 200 pph silica powder was aged under accelerated conditions for 100 h (100 to 250°C) and then its tracking resistance was assessed. The tracking resistance of CAE that was exposed to water absorption (0 to 3.3%) also is evaluated. Changes on the surface layer (1 to 10 μm) with thermal treatment are revealed by employing scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analysis, attenuated total reflection (ATR)-Fourier transform infrared (FTIR), reflective visible spectroscopy and thermal gravimetry (TG)-differential thermal analysis (DTA) mass spectrometry (MS). The tracking resistance of CAE aged above 170°C is particularly reduced. Surface resistivity declines with rising temperature of thermal aging. The lowering of surface resistivity enlarges the leakage current passing at the aged surface layer and increases the surface temperature of CAE. This would accelerate thermal aging. It also is shown that absorbed water in CAE decreases tracking resistance. The effect of absorbed water during the initial stage of a tracking test is described. Under saline pollution and moisture, thermal aging affects not only surface tracking but also electrochemical erosion derived from sodium hydroxide which forms through electrolysis of sodium chloride. Electrochemical erosion enhances water uptake for CAE, which can lead to tracking resulting from absorbed water     

Progress in the smart pixel technologies

The purpose of this paper is to review the recent progress in the developing smart pixel technologies. The paper begins by reviewing some of the rapidly evolving smart pixel terminologies. It then describes several of the smart pixel technologies that have recently emerged. Finally, it outlines the performance of these technologies in both device complexity and aggregate capacity. The reviewed SPA technologies include both the modulator-based FET-SEED, hybrid CMOS-SEED, and LCOS smart pixels and the source-based hybrid VCSEL/MSM, ELO, flip-chip-bonded VCSEL/MSM, and monolithic MSM/MESFET/VCSEL smart pixels