Yongbo Su

Self-assembly and magnetic properties of cobalt nanoparticles

Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles.

Synthesis and characterization of n-octadecayl mercaptan-protected palladium nanoparticles

Long-chain n-octadecayl mercaptan (C18H37SH)-passivated palladium nanoparticles are synthesized and characterized. The palladium nanoparticles are successfully capped by n-octadecayl mercaptan. These palladium nanoparticles have the same face-centered cubic crystalline structure as Pd in the bulk phase. The size of the capped palladium nanoparticles varies in the range of 1.3–5.5 nm for various reaction conditions. These results show that the long-chain n-octadecayl mercaptan-capped palladium nanoparticles are more stable than alkanethiolate-capped Pd nanoparticles with a shorter chain. 2003 Elsevier Science B.V. All rights reserved.

Study of AlN dielectric film on graphene by Raman microscopy

Dielectric film on graphene severely affects the performance of graphene field-effect transistors (GFETs). The authors investigated AlN dielectric film on graphene by Raman microscopy. AlN deposition led to the appearance of disorder-related peaks and to a wider Raman-active peak. The intensities of the disorder-related modes decreased exponentially with an increase in the layer number of graphene, indicating that AlN dielectric film mainly affected the surface of graphene. According to the experimental results, the authors suggested that few-layer graphene might be a better choice than single-layer graphene for the application of GFET.

A Combined Model With Electrothermal Coupling and Electromagnetic Simulation for Microwave Multifinger InP-Based DHBTs

This paper presents a combined model with electrothermal coupling and electromagnetic (EM) simulation for multifinger InP-based double heterojunction bipolar transistors (DHBTs). The electrothermal coupling effect, which occurs in multifinger InP DHBTs, is characterized based on 3-D thermal simulation. In addition, EM simulation technique is presented to account for the distributed effect of interconnection of the fingers and their surroundings. A large-signal model for single-finger DHBTs is implemented as a seven-port symbolically defined device, which accounts for several physical phenomena, including the self-heating effect, Kirk effect, current blocking effect, mobile charge modulation of the base-collector capacitance, and velocity field modulation in the transit time. The combined model implemented in Agilent-ADS is verified by comparing the simulated and measured data in dc small-signal S-parameters and large-signal microwave power characteristic. This approach allows a simple method to analyze and predict microwave multifinger InP DHBTs for power amplifier circuit design using commonly available computer-aided design tools such as Agilent-ADS.

An InGaAs/InP 40 GHz CML static frequency divider

Static frequency dividers are widely used as a circuit performance benchmark or figure-of-merit indicator to gauge a particular device technologys ability to implement high speed digital and integrated high performance mixed-signal circuits. We report a 2 : 1 static frequency divider in InGaAs/InP heterojunction bipolar transistor technology. This is the first InP based digital integrated circuit ever reported on the mainland of China. The divider is implemented in differential current mode logic (CML) with 30 transistors. The circuit operated at a peak clock frequency of 40 GHz and dissipated 650 mW from a single −5 V supply.

A 79 GHz sub-harmonic mixer design using a 1 um InP DHBT technology

This paper presents a 79 GHz sub-harmonic mixer (SHM) design based on a self-developed 1 um InP DHBT process. In this design, a low frequency local oscillator (LO) input signal at 39.5 GHz is doubled to W-band and a radio frequency (RF) signal ranging from 80 GHz to 86 GHz is down-converted to the intermediate frequency (IF) band with a best conversion gain around 1 dB at 83 GHz. As the knowledge of authors, it is the first attempt to implement an InP DHBT based SHM with a LO doubler in W-band. Due to lacking of available RF sources, the testing is realized with one port of an output power fixed Vector Network Analyzer enhanced by a frequency up-conversion module.

An improved VBIC model for InP DHBTs

An emprical model is established for InP/InGaAs DHBTs based on the VBIC model. The heterojunction barrier and current blocking effect are considered in the current expressions. And new empirical models for transit time and collector capacitance are proposed by considering the voltage and current dependence. The excellent fitting results show that the improved model has better accuracy than the conventional VBIC model.

A 20-dB gain W-band InP DHBT power amplifier

A two-stage double heterojunction bipolar transistor (DHBT) power MMIC fabricated in InP technology is realized using coplanar waveguide structure. The output cell unit consists of four parallel cascode fingers. Sixteen fingers are at output stage from which the power is combined. Broad-band, low-loss matching networks lead to high gain and high combining efficiency. The chip area is 1.5×1.7 mm2. Measurements show that small signal gain is above 20 dB over 75.5 GHz ~ 84.5 GHz frequency band. Simulated saturated power is 19.7 dBm @ 89 GHz and the actual output power is to be measured once the W-band power source arrive.

A 75 GHz regenerative dynamic frequency divider with active transformer using InGaAs/InP HBT technology

This letter presents a high speed 2:1 regenerative dynamic frequency divider with an active transformer fabricated in 0.7 μ m InP DHBT technology with f T of 165 GHz and f max of 230 GHz. The circuit includes a two-stage active transformer, input buffer, divider core and output buffer. The core part of the frequency divider is composed of a double-balanced active mixer (widely known as the Gilbert cell) and a regenerative feedback loop. The active transformer with two stages can contribute to positive gain and greatly improve phase difference. Instead of the passive transformer, the active one occupies a much smaller chip area. The area of the chip is only 469×414 μ m 2 and it entirely consumes a total DC power of only 94.6 mW from a single -4.8 V DC supply. The measured results present that the divider achieves an operating frequency bandwidth from 75 to 80 GHz, and performs a -23 dBm maximum output power at 37.5 GHz with a 0 dBm input signal of 75 GHz.

An 89 GHz single-balanced mixer design in 1 um InP DHBT technology

This paper demonstrates an active single-balanced mixer with InP double heterojunction bipolar transistor (DHBT) process for direct down-conversion system at 89 GHz. Authors use Coplanar Waveguide (CPW) as on-chip transmission line and tune an on-chip CPW balun to allocate LO signal to the switch cell. Benefiting from its balanced structure, this mixer shows a LO port to RF port isolation above 20 dB in all W-band. Its conversion gain is up to 3 dB with a 3 dB RF bandwidth more than 10 GHz. With a 10 dBm LO signal, the RF input 1 dB compression point is higher than -4 dBm around 89 GHz. This mixer consumes 340 mW power with a +4 V supply. All wafers have been thinned to 100 um before measurements.