Kinjiro Kosemura

Room temperature operation of Si single-electron memory with self-aligned floating dot gate

We have developed an excellent fabrication method for a Si single-electron field effect transistor memory device having a self-aligned floating dot gate. This device demonstrates single electron memory operation at room temperature. The ability to precisely control the size and position of the floating dot gate and the channel indicates the feasibility of practical single-electron memory.

Short-channel effects in subquarter-micrometer-gate HEMTs: simulation and experiment

The authors studied the electrical properties of subquarter-micrometer-gate HEMTs (high electron mobility transistors) by Monte Carlo simulation and experiment. Simulation shows that subquarter-micrometer-gate HEMTs have extremely high performance, and the near-ballistic movement under the gate was confirmed. It is also shown that the aspect ratio of the channel could be used as a guide to determine the extent of short-channel effects. The transverse-domain formation inherent in short-channel HEMTs may also contribute to the smaller short-channel effect by limiting undesirable substrate current. Experimentally, only a negligible short-channel effect was observed when the gate length was reduced from 1.25 to 0.14 mu m. Thus it is not necessary to design and fabricate a special structure for HEMTs, as such a structure might have limited applications. >

Si single electron tunneling transistor with nanoscale floating dot stacked on a Coulomb island by self-aligned process

We fabricated a Si single electron tunneling transistor which has a nanoscale floating dot gate stacked on a Coulomb island by a self-aligned process. This device exhibits drain current (Id) oscillations due to the Coulomb blockade effect and quantized threshold voltage (Vth) shifts resulting from a single electron tunneling from the channel to the floating dot gate. The high on/off current ratio of the Id oscillation combined with the quantized Vth shifts leads to the possibility of developing ultralow power consumption memory.

New phase-shifting mask with highly transparent SiO2 phase shifters

A phase-shifting mask enables subhalf-micron optical lithography. We propose a new phase-shifting mask with Si02 phase shifters. Si02 phase shifters on a quartz mask substrate have the advantages of low absorption under deep UV and a lack of multiple interference. Si02 phase shifters were fabricated by lift-off of the evaporated Si02 film. The new phaseshifting mask is highly transparent to deep UV and provides a 2 uniformity of phase shift over the full exposure field of a 5X stepper. Improved resolution of 0. 25 im lines and spaces was achieved by using a KrF excimer laser stepper and the new phase shifting mask. We also characterize the image profile projected with a phase-shifting mask because the reproducibility of mask features on a wafer declines when a phase-shifting mask is used. We indicate the importance of the interference between the main and side lobes of diffraction patterns for individual apertures and clarify the mechanism ofreproducibility degradation in optical lithography using a phase-shifting mask. 1.

Si single-electron tunneling transistor with nanoscale floating dot stacked on a Coulomb island by self-aligned process

We studied experimentally and theoretically in detail a Si single-electron tunneling transistor which has a nanoscale floating dot gate stacked on a Coulomb island by a self-aligned process. At 4.2 K, this device exhibits drain current (Id) oscillations due to the Coulomb blockade effect besides the quantized threshold voltage (Vth) shifts with a hysteresis resulting from a single-electron tunneling between the channel and the floating dot gate. The periodicity of the Coulomb oscillation, the voltage separation (ΔVw) between the adjacent two voltages where the Vth shift occurs are consistent with those calculated from the geometrical consideration. The Coulomb oscillation disappeared at room temperature, however, the quantized Vth shifts and hysteresis curves, which are basic operations of single-electron memory, were observed up to room temperature. The fluctuation of electron number in the floating dot was theoretically analyzed at room temperature and we obtained consistent results with the experiments...

Cost-effective 60-GHz modules with a post-wall planar antenna for gigabit home-link systems

Cost-effective 60 GHz modules were developed for home-link systems which needed the bit rate of several Gbps. The modules are composed of a packaged MMIC mounted on the printed circuit board and a post-wall planar antenna formed on the backside of the board. The antenna gain is 20 dBi. The board with the size of 75 × 32 × 1.2 mm3 is inserted into the card-edge connector to feed the IF signal and the DC power. The module can be characterized to have no mm-wave terminals. When the output power of the transmitter module ( Tx ) was 8 dBm at 61.0 GHz, the IF output power of the receiver module ( Rx ) PIFout was ¿37 dBm at the distance D = 10 m between Tx and Rx. This experiment suggests the capability of the transmission with the bandwidth of 2.5 GHz and the C/N of 25 dB in the home-link systems.

Electron waves through quantum point contacts

This paper reviews the authors work on the experimental and theoretical analyses of the angular distribution of electrons injected through a single quantum point contact. They observed double peaks in the distribution with the point contact quantized in two modes. The authors calculation of the distribution using a Fraunhofer diffraction approximation through a quantized single slit agreed well with results. In this calculation they use a Greens function in weak magnetic fields and constructed mirror images there. They also investigated the possibility of observing interference in the angular distribution between the first and second modes, and found that the interference terms of the angular distribution were cancelled due to system symmetry. Another possible way to observe interference is due to electron waves through double point contacts. To measure this interference, the authors developed submicron air bridges to make double point contacts with independently controlled widths. The authors measured the controlled additivity of the conductance for four point contacts.

Additivity of the Quantized Conductance of Multiple Parallel Quantum Point Contacts

We report on the first direct observation of the additivity of the quantized conductance for multiple parallel quantum point contacts. We have studied from 1 to 4 parallel quantum point contacts and find that the total conductance can be written in the form (2e2NLNQPC/h) as a function of the applied gate voltage, where NQPC is the number of parallel quantum point contacts. The processing of multiple parallel quantum point structures is also described.

Angular distribution of electrons injected through a quantum point contact

Abstract This paper reports on the measurement of the angular distribution of electrons injected through a quantum point contact. We observed double peaks in the distribution with the point contact quantized in two modes. Our calculation of the distribution using an approximation of Fraunhofer diffraction through a quantized single slit agreed well with results. This paper also discusses the interference between the first and second modes, and shows how the terms of interference in the angular distribution are canceled.

EB lithography for fabricating a GHz SAW filter on LiTaO3 substrate (Poster Paper)

We fabricated 2.6 GHz surface acoustic wave (SAW) filters using an electron beam exposure system. The filter consists of an interdigital transducer of aluminum on piezoelectric material (LiTaO3). Since the LiTaO3 density was high, a large number of electrons were backscattered from the material when exposed by electron beams. When a conventional negative resist was used, the backscattered electrons degraded the image contrast so that resist residue remained on unexposed areas after development. The process margin, which indicates exposure tolerance, was calculated. The process margin was small for LiTaO3, indicating that it is difficult to suppress resist residue when negative resist is used and that a positive resist should be used. To obtain vertical walls of positive resist, we used a 0.4-micrometers double-layer configuration in which the upper layer had a lower sensitivity than the bottom layer. To prevent the piezoelectric substrate from breaking due to the pyroelectric effect, the resist pre- and post-baking temperature was raised gradually at a rate of 5 degrees/minute. The 0.4-micrometers line and space patterns required for a 2.6 GHz filter could be produced accurately. The fabricated SAW filter had a 2.58 GHz center frequency and an insertion loss of 5.0 dB.