Improving the characteristics of InAlAs/InGaAs heterojunction bipolar transistors by employing thin base and collector layers

InAlAs/InGaAs heterojunction bipolar transistors with thin base and collector layers are fabricated. The maximum value of current gain cutoff frequency is as high as 96 GHz. It is shown that thinning of the base and collector is very effective not only for reducing the base and collector transit times but also for suppressing the space charge effect in the collector.<>     

Dynamic Characteristics Analysis of Two‐DOF Oscillatory Actuator and Experimental Verification of Prototype

Recently, linear oscillatory actuators have been used in a wide range of applications. In particular, small linear oscillatory actuators are expected to be used in haptic devices by being extended to provide multi‐degree‐of‐freedom motion with arbitrary acceleration. In this paper, we propose a compact two‐DOF oscillatory actuator that can move in various directions on a plane. The static and dynamic characteristics of the actuator are determined by the 3D finite element method. The effectiveness of this method is shown through a comparison of the measured results with the experimental results from a prototype. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 58–65, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22312     

VLSI implementation of a variable-length pipeline scheme fordata-driven processors

A VLSI-oriented variable-length pipeline structure for data-driven processors is presented. Ordinary inline pipelines have the problem of minimizing the average total processing time through the pipeline, since subdivision of a function along the pipeline is usually optimized for the most complex operations in spite of the fact that simpler operations need fewer stages. As a solution to this problem, a variable-length pipeline scheme in which data go through only the necessary stages according to information contained within is proposed. The scheme has been implemented on a test chip to verify performance. The chip demonstrated a minimum fall-through time (data transmission time from input to output) of 14.4 ns and a data transmission rate in the pipeline of 59 megaword/s (that is, 1/16.9 ns) as a first-in first-out (FIFO) store. By modifying the data transfer control and allocating the processing functions corresponding to the data interval of 16.9 ns, this scheme is applicable as a high-performance processing unit for data-driven processors     

Structural studies of enzyme-based microfluidic biofuel cells

An enzyme-based glucose/O₂ biofuel cell was constructed within a microfluidic channel to study the influence of electrode configuration and fluidic channel height on cell performance. The cell was composed of a bilirubin oxidase (BOD)-adsorbed O₂ cathode and a glucose anode prepared by co-immobilization of glucose dehydrogenase (GDH), diaphorase (Dp) and VK₃-pendant poly-l-lysine. The consumption of O₂ at the upstream cathode protected the downstream anode from interfering O₂ molecules, and consequently improved the cell performance (maximum cell current) ca. 10% for the present cell. The cell performance was also affected by the channel height. The output current and power of a 0.1 mm-height cell was significantly less than those of a 1 mm-height cell because of the depletion of O₂, as determined by the shape of the E–I curve at the cathode. On the other hand, the volume density of current and power was several times higher for the narrower cell.     

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55-μm wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device     

A majority-logic device using an irreversible single-electron box

We describe a majority-logic gate device suitable for use in developing single-electron integrated circuits. The device consists of a capacitor array for input summation and an irreversible single-electron box for threshold operation. It accepts three binary inputs and produces a corresponding output, a complementary majority-logic output, by using the change in its tunneling threshold caused by the input signals; it produces a logical 1 output if two or three of the inputs are logical 0 and a logical 0 output if two or three of the inputs are logical 1. We combined several of these gate devices to form subsystems, a shift register and a full adder, and confirmed their operation by computer simulation. The gate device is simple in structure and powerful in terms of implementing digital functions with a small number of devices. These superior features will enable the device to contribute to the development of single-electron integrated circuits.     

Pulsed laser action in Tm,Ho:LuLiF/sub 4/ and Tm,Ho:YLiF/sub 4/ crystals using a novel quasi-end-pumping technique

A number of good quality thulium and holmium-codoped LuLiF/sub 4/ and YLiF/sub 4/ single crystals were successfully grown by the Czochralski crystal growth method under a CF/sub 4/ atmosphere. Using a novel diode-pumped, quasi-end-pump scheme incorporating two lens ducts, pulsed laser action is achieved in 5%Tm, 0.5% Ho:LuLiF/sub 4/ and 5%Tm, 0.5% Ho:YLiF/sub 4/ crystals, at various pulse repetition frequencies and temperatures. At 10 Hz and at an operating temperature of 273 K, slope efficiencies (optical to optical efficiencies) with respect to the incident pump energies of 12.9% (9.2%) and 7.4% (5.2%) were demonstrated in the grown Tm, Ho:LuLiF/sub 4/ and Tm, Ho:YLiF/sub 4/ crystals, respectively. Free running laser output energies in excess of 30 mJ (LuLiF/sub 4/) and 17 mJ (YLF) were measured.     

An InGaAs/InAlAs superlattice avalanche photodiode with a gain bandwidth product of 90 GHz

The authors describe the fabrication of an InGaAs/InAlAs superlattice avalanche photodiode with a gain-bandwidth product of 90 GHz. The device is composed of an InGaAs/InAlAs superlattice multiplication region and an InGaAs photoabsorption layer. The effect of the superlattice multiplication region thickness on the gain-bandwidth product was studied. A gain-bandwidth product of 90 GHz was obtained for the device with a multiplication region thickness of 0.52 mu m. Low noise performance is compatible with the high gain-bandwidth product due to improvement of the ionization rate ratio made by introducing a superlattice structure into the multiplication region.<>     

Observation of low-chirp modulation in InGaAs-InAlAs multiple-quantum-well optical modulators under 30 GHz

Modulated light spectra were measured in long-wavelength InGaAs-InAlAs multiple-quantum-well intensity modulators under 30-GHz large-signal modulations. The linewidth broadening factor alpha is determined from the relation between the intensity modulation index and the sideband strength relative to the carrier. The minimum alpha value is estimated to be 0.70 at 1.54 mu m, which is almost the same as the lowest value so far reported in a bulk Franz-Keldysh modulator. This is significantly lower than what is obtained from direct-intensity modulation of injection lasers, making this a useful device for application to high-bit-rate long-haul optical communication systems.<>