Shigeharu Kimura

Silicon on thin BOX: a new paradigm of the CMOSFET for low-power high-performance application featuring wide-range back-bias control

We demonstrate a new MOSFET on ultra-thin BOX that allows wide-range back-bias control in low-power and high-performance applications. The back gate is effective not only to increase the drive current by about 20% in active mode but also in reduce the off-current by an order of magnitude in stand-by mode. We have also demonstrated tunable-threshold-voltage technology for devices with metal gates and ion implantation for V/sub th/ control. The target V/sub th/ for low-power applications was achieved by using ion implantation for V/sub th/ control. We propose a 6-transistor SRAM memory cell in which we obtain even more benefit from the new device structure by adding a feedback mechanism. A proposed 6-Tr SRAM memory cell is shown to dramatically improve SNM characteristics at the 65-nm technology nodes, and this effect will also apply at finer nodes.

Confocal scanning optical microscope using single-mode fiber for signal detection

A single-mode fiber is employed as a detector in a confocal scanning optical microscope (CSOM) instead of a pinhole and its optical property is studied. The optical system is always coherent, which is fundamentally different from the CSOM with a finite-sized pinhole. The coherent transfer function and the axial response are calculated. Experimentally, the coherent image is taken and the axial response is also measured.

Limitations and challenges of multigigabit DRAM chip design

This paper describes the limitations and challenges involved in designing gigabit DRAM chips in terms of high-density devices, high-performance circuits, and low-power/low-voltage circuits. The key results obtained are as follows. 1) For formation of a MOSFET shallow junction, which suppresses threshold voltage (V/sub T/) variation and offset voltage of sense amplifiers, reduction in ion-implantation energy and process temperature is essential. Also, the keys in terms of area, speed, stable cell operation, and ease of fabrication are use of low-resistivity multilevel metal wiring and high permittivity materials and three-dimensional memory cells to reduce a difference in height between the memory cell array and the surrounding peripheral circuits. 2) For creation of a high speed, the keys are memory-subsystem technology such as pipeline operation, wide-bit I/O, low-voltage interfaces, and high-density packaging. Embedded DRAM further enhances the speed and throughput by using massively parallel processing of signals on a large number of data-lines and reducing internal bus capacitances. 3) For power reduction, the key continues to be reduction of the data-line dissipating charge through both partial activation of multidivided data-lines and lowering of the data-line voltage. Ultralow-voltage operation, essential to drastic power reduction, can be achieved by subthreshold-current reduction circuits such as source-gate backbiasing, multi-V/sub T/, dynamic V/sub T/, and node-boosting schemes.

Performance enhancement of strained-Si MOSFETs fabricated on a chemical-mechanical-polished SiGe substrate

Chemical-mechanical-polishing (CMP) was used to smooth the surface of a SiGe substrate, on which strained-Si n- and p-MOSFETs were fabricated. By applying CMP after growing the SiGe buffer layer, the surface roughness was considerably reduced, namely, to 0.4 nm (rms). A strained-Si layer was then successfully grown on the CMP-treated SiGe substrate. The fabricated strained-Si MOSFETs showed good turn-off characteristics, (i.e., equivalent to those of Si control devices). Moreover, capacitance-voltage (CV) measurements revealed that the quality of the gate oxide of the strained-Si devices was the same as that of the Si control devices. Flat-band and threshold voltages of the strained-Si devices were different from those of the Si control devices mainly due to band discontinuity. Electron and hole mobilities of strained-Si MOSFETs under a vertical field up to 1.5 MV/cm increased by 120% and 42%, respectively, compared to the universal mobility. Furthermore, current drive of the n- and p-MOSFETs (L/sub eff//spl ges/0.3 /spl mu/m) was increased roughly by 70% and 50%, respectively. These improvements in characteristics indicate that CMP of the SiGe substrate is a critical technique for developing high-performance strained-Si CMOS.

The impact of data-line interference noise on DRAM scaling

A kind of data-line (DL) interference noise in a scaled DRAM cell array is found and studied through analysis. The dynamic behavior of cell arrays due to sense-amplifier operation is derived analytically. Analysis shows that the amount of interference noise is more than three times larger than expected from simple data-line coupling. A novel experimental technique for precise noise determination is developed to verify the analysis. Analytical results are in good agreement with the experimental data. It is found that the interference noise plays a dominant role in determining the operating margin of the DRAM and that a novel process or a cell array architecture for minimizing the interference noise is indispensable in 16-Mb DRAM and beyond. >

Calculation of three-dimensional optical transfer function for a confocal scanning fluorescent microscope

A confocal scanning fluorescent microscope is suitable for 3-dimensional (3-D) imaging. The 3-D optical transfer functions (OTF’s) for such a microscope are calculated to show their dependence on the wavelength of the fluorescence. These calculations reveal that when the wavelength of the fluorescence is equivalent to that of the excitation light, the 3-D OTF has no missing-cone region. However, as the wavelength becomes longer, the 3-D OTF approaches that of an incoherent conventional microscope at the wavelength of the excitation light.

Smallest V th variability achieved by intrinsic silicon on thin BOX (SOTB) CMOS with single metal gate

A ldquosilicon on thin BOXrdquo (SOTB) CMOS with a 50-nm single metal (FUSI) gate has been developed. By employing an intrinsic channel and a metal gate, this SOTB achieves the smallest Vth variability ever reported. The measured Pelgrom coefficients of the SOTB were 1.8 and 1.5 for NMOS and PMOS, respectively, even in the case of relatively thick EOT of 1.9 nm. Both multi-Vth control as well as suppression of short-channel effects were carried out simply by adjusting the impurity concentration beneath the BOX layer while keeping the channel almost intrinsic. Inverter delay and off-current were optimized by controlling gate-overlap length by means of a dual-layer offset spacer. It is shown that, within planar-type low-power CMOS devices, the SOTB is the most scalable because of its capability of multi-Vth and excellent matching characteristics.

A new stacked cell structure for giga-bit DRAMs using vertical ultra-thin SOI (DELTA) MOSFETs

Summary form only given. The first stacked DRAM (dynamic RAM) cell using vertical ultra-thin SOI (silicon-on-insulator) MOSFET (DELTA, or fully depleted lean-channel transistor) is proposed. Since the ultra-thin SOI structure provides high noise immunity, the storage node capacitance can be reduced by more than 50%. Therefore, in the proposed DRAM cell a large storage capacitor need not be essential, and this will extend the DRAMs miniaturization to the gigabit levels. The cell structure schematic is shown and threshold voltage dependences on channel length of DELTA-, conventional NMOS-, and PMOS-FETs are demonstrated. DELTA shows good short channel characteristics compared to conventional NMOS.<<ETX>>

A new stacked capacitor DRAM cell characterized by a storage capacitor on a bit-line structure

The authors introduce a diagonal active stacked capacitor cell with a highly packed storage node (DASH) for use in a 16-Mb DRAM (dynamic random access memory). This novel cell features a storage capacitor formed above a bit line and the diagonal active area, which provides a large storage capacitance, 35 fF/bit, in a cell size of 3.4 mu m/sup 2/. The average charge retention time measured using an experimental 2-kb array is 30 s at 40 degrees C, indicating that the DASH has a superior potential for application to 16-Mb DRAMs. The memory cell leakage current is controlled to the order of 10/sup -12/ A.<<ETX>>

A 60-ns 16-Mbit CMOS DRAM with a transposed data-line structure

Low-noise, high-speed circuit techniques for high-density DRAMs (dynamic random-access memories), as well as their application to a single 5-V 16-Mb CMOS DRAM with a 3.3-V internal operating voltage for a memory array, are described. It was found that data-line interference noise becomes unacceptably high (more than 25% of the signal) and causes a serious problem in 16-Mb DRAM memory arrays. A transposed data-line structure is proposed to eliminate the noise. Noise suppression below 5% is confirmed using this transposed data-line structure. A current sense amplifier is also proposed to maintain the data-transmission speed in common I/O lines, in spite of a reduced operating voltage and increased parasitic capacitance loading in the memory array. A speed improvement of 10 ns is achieved. Using these circuit techniques, a 16-Mb CMOS DRAM with a typical RAS access time of 60 ns was realized. >