Fan-Hsiu Huang

High-performance evanescently edge coupled photodiodes with partially p-doped photoabsorption layer at 1.55-/spl mu/m wavelength

In this letter, we demonstrate a high-performance evanescently coupled photodiode (ECPD) with the partially p-doped photoabsorption layer. As compared to the control ECPD with the traditional intrinsic photoabsorption layer, the demonstrated device can exhibit much higher output saturation current (power) and electrical bandwidth without sacrificing the quantum efficiency performance. By properly designing the geometry size and epilayer structures of the partially p-doped ECPD, very high responsivity (1.01 A/W), high electrical bandwidth (around 50 GHz), and high saturation current bandwidth product (920 mA/spl middot/GHz, at 40 GHz) have been achieved simultaneously at 1.55-/spl mu/m wavelength.

Photonic crystal directional couplers formed by InAlGaAs nano-rods.

This study demonstrates the use of photonic crystal directional couplers to separate light of wavelengths 1.31 and 1.55microm. The photonic crystal structure consists of InAlGaAs nano-rods arranged in square lattice. The coupling length of the light in the directional coupler at a wavelength of 1.31microm was designed to be four times greater than that at 1.55microm. This behavior helps in designing devices to split the two wavelengths. The devices are fabricated by e-beam lithography and conventional photolithography. The measurement results confirm that 1.31microm/1.55microm directional couplers can be realized in PC structures formed by nano-rods.

Separated-transport-recombination p-i-n photodiode for high-speed and high-power performance

We demonstrate a novel p-i-n photodiode (PD) structure, the separated-transport-recombination PD, which can greatly relieve the tradeoffs among the resistance-capacitance bandwidth limitation, responsivity, and output saturation power performance. Incorporating a short carrier lifetime (less than 1 ps) epitaxial layer to serve as a recombination center, this device exhibits superior speed and power performance to a control PD that has a pure intrinsic photoabsorption layer. Our demonstrated structure can also eliminate the bandwidth degradation problem of the high-speed photodetector, whose active photoabsorption layer is fully composed of short lifetime (/spl sim/1 ps) materials, under high dc bias voltages.

Low-/spl kappa/ BCB passivation on AlGaN-GaN HEMT fabrication

Due to the stress-induced polarization effect on the GaN HEMTs, the surface passivation of the device is critical and is deserved to conduct a detailed study. It has been proven that the GaN HEMTs demonstrate nondispersive pulsed current-voltage (I-V) characteristics and better microwave power performances after passivating the Si/sub 3/N/sub 4/ film on the GaN surface. In this letter, we proposed to use the BCB material, a negative photoresist with a low-/spl kappa/ characteristic, as the surface passivation layer on GaN HEMTs fabrication. After comparing the dc I-V, pulsed I-V, RF small-signal, microwave power characteristics, and device reliability, this BCB-passivated GaN HEMT achieved better performance than the Si/sub 3/N/sub 4/ passivated device.

A

This study presents a W-band injection-locked frequency divider (ILFD) with a wide locking range characteristic by using 0.15 mum GaAs pHEMT techniques. Based on the cascode circuit topology, the oscillation and the injection parts can be designed individually without the trade-off between the input matching and the oscillation condition. Including with a characteristic of the active capacitance in this ILFD, a free-running oscillation frequency about 50 GHz was obtained with a frequency tuning function, in which the tuning range was about 1.2 GHz (50.5-49.3 GHz). By injecting a signal of around 100 GHz into this ILFD, the maximum locking range was measured up to 400 MHz, while the injected power was set to -5 dBm under a 3 V supply with a power consumption of 21 mW in the ILFD core.

W

While the operation frequency of the wireless and the wire-used modern communication systems has being extended to millimeter-wave band, the timing circuits also become important for the low-cost and performance concerns, such as synthesizer or frequency divider. As the millimeter-wave wireless local area network (WLAN) transmitting a digital modulated data upon a carrier frequency through a antenna, is proposed to either obtain a broadcasting service in local area or provide the flexible data access. For the requirement of synchronization, hence the high speed and high frequency dividers/prescalars up to 60 GHz may be employed in phase-locked loop (PLL). Moreover, the power consumption and the low noise features in the divider circuits are also the major concerns. Conventional common-mode logic (CML) dividers are difficult to push the maximum operation frequency to over the microwave range due to its limitation by the cut-off frequency fT, regardless it reaches a wide dividing range. Extreme high power consumption is also the disadvantage for CML approach. Thus to fulfil the low power dissipation dividers, the LC-type injection-locked frequency dividers (ILFD) have been proposed and being used in PLL or clock-data recovery (CDR) circuits as stated in H. R. Rategh et al. (1999). The CMOS submicron techniques have been progressed to a proper high frequency divider design. In this work, there are two 60 GHz ILFDs have been realized by using the CMOS 0.18mum 1P6M technology, in which contain the self-oscillation frequencies of 30 GHz and 15 GHz respectively for a divided-by 2 or 4 operation. Both ILFDs demonstrate the improved locking ranges using a self-oscillation frequency tuning and a 0/180deg single-to-differential power divider with low dc power consumptions

-band Injection-Locked Frequency Divider Using GaAs pHEMTs and Cascode Circuit Topology

We demonstrate a novel structure of electroabsorption modulator (EAM) at a 1.55-/spl mu/m wavelength: the dual-depletion-region EAM. After an n/sup +/ delta-doped layer was inserted into the thick intrinsic region (550 nm) of a tradition p-i-n modulator, the tradeoff between driving-voltage and electrical bandwidth performance can be released effectively. This new structure can also release the burden imposed on downscaling the width or length of high-speed EAM with low driving-voltage performance. The microwave and electrical-to-optical measurement of this novel device with traveling-wave electrodes show very convincing results.

V-Band CMOS Differential-type Injection Locked Frequency Dividers

A V-band CMOS injection-locked oscillator (ILO) based on a cross-coupled oscillator configuration containing nMOS and pMOS devices is implemented by using 0.18 mum CMOS process. This ILO has a free-running output frequency around 60 GHz while the double push-push technique was used as a frequency multiplier. It also has a wide output locking bandwidth of up to 3.64 GHz (from 59.36 to 63 GHz) as injecting a signal near 15 GHz with the fundamental injection-locked behavior. Controlling the output frequencies by the injected signals, the output signal has a phase noise of 108 dBc/Hz at a 1 MHz offset with consuming only 9.8 mW dc power under a 2 V supply.

Demonstration of a dual-depletion-region electroabsorption modulator at 1.55-/spl mu/m wavelength for high-speed and low-driving-voltage performance

A V-band cross-coupled sub-harmonic injection-locked oscillator has been designed and fabricated using 0.15-mum GaAs pHMET technology. Based on the known harmonic injecting circuit topology, this oscillator was designed by a differential output approach, a low-Q microstrip-line resonator, and a current mirror, which has a free-running oscillation frequency around 60GHz with a tuning range of 2.5GHz (from 57.8GHz to 60.3GHz). The maximum single-end output power is 3.8dBm with a dc dissipation of 225mW under a -3V supply voltage. Within the input matching network for second (30GHz) and fourth (15GHz) sub-harmonic signals injection, it demonstrates the maximum locking ranges close to 120MHz and 30MHz, respectively

A

In this paper, we developed dual-gate enhancement/enhancement-mode (E/E-mode) and enhancement/depletion-mode (E/D-mode) AlGaAs/InGaAs pHEMTs for high-voltage and high-power device applications. These dual-gate devices had a higher breakdown voltage (Vbr) and maximum oscillation frequency (fmax). This could be obtained because there were two depletion regions, and the total electrical field was shared between the two regions, leading to lower output conductance (go) and lower gate-to-drain capacitance (Cgd). The dual-gate device can be operated at a higher drain-to-source voltage (Vds), resulting in better linear gain and output power performance, as compared to a conventional single-gate E-mode GaAs pHEMT device. The maximum oscillation frequency obtained using the dual-gate E/E-mode device increased from 78 to 123 GHz. When operated at 2.4 GHz, the maximum RF output power of the single-gate E-mode and dual-gate E/D-mode devices increased from 636 to 810 mW/mm, respectively. We also produced a 2.4-GHz high-gain and high-power density two-stage power amplifier using dual-gate E/E and E/D-mode transistors. A linear gain of 40 dB and a maximum output power of 24 dBm were obtained.