Chief Research Performance

1.1 R&D for CMOS technology with new material and structure

Achieved world-class level current value and hole mobility of germanium (Ge) nano-wire transistor

Prototype of MOS transistor with channel (current pathway) of 20mm width Ge nano-wire was created, and observed significantly high hole mobility compared with existing silicon (Si). This was resulted from introduction of large strain into Ge crystal lattice in addition that Ge channel has higher mobility than that of Si. Consequently, world-class current value was achieved in comparison with existing device of similar structure. Based on this successful work, achievement of ultralow-power LIS which operates with low voltage is looked forward to.

Cross-sectional image by transmission electron microscope
Cross-sectional image by transmission electron microscope
Hole mobility of prototype transistor
Hole mobility of prototype transistor

1.2 R&D for CMOS device with new operating principle

Demonstrate steep switching property of SS=33mV/decade

新動作原理CMOSデバイスの研究開発イメージ 新動作原理CMOSデバイスの研究開発イメージ

Transistor switching property is showed by gate voltage SS value necessary for changing power current by single digit. Theoretical limitation for existing FET is SS=60mV/decade. But, the smaller this value is, the drain current changes significantly according to small change of gage voltage, and steep switching property is obtained. By adopting the thinned gate insulator film (0.9mm with SiO2 equivalent thick film) and steep dopant profile by flashlamp annealing, a tunnel transistor (TFEF) with steep as SS=33mV/decade switching property was successfully achieved. On these results, we are carrying forward our research in order to achieve higher drive current and steeper switching property by introducing new semiconductor materials and so on.

Developed new simulator for predicting transistor property


TCAD (Technology CAD) is an important simulation tool for predicting the transistor property. Because the TCAD has been manufactured based on the existing transistor, any new materials or structures – especially electronic behavior under intense electric field such as tunnel transistor (TFET) – have not been taken in consideration.

In 2011, we have developed simulation module with which precise prediction of TFET Property can be feasible. To achieve this result, we conducted precise modeling of interband transition process as well as dynamic lookup at the tunnel direction. This module is being mounted on the HyENEXSSTM TM※TCAD to seek feasibility of 3D channel TFET, or predict performance of TFET made from new semiconductor materials.

※ HyENEXSS™, ver. 5.5, Selete, 2011

2.1 Synthesizing graphene and applying to transistor

Arrival of semiconductor made from grapheme by irradiation of helium ion

Graphene has high mobility and expected to apply to transistor channel. But, as graphene has no band gap, high on-off ratio is unobtainable when applied to transistor. First time in the world, we have succeeded to form transport (Drain) gap in graphene by irradiating it with helium ion. Also, we manufactured a transistor with channel of helium-irradiated graphene and achieved high on-off ratio in room temperature.

S. Nakaharai et al., SSDM 2012

Arrival of semiconductor made from grapheme by irradiation of helium ion
Arrival of semiconductor made from grapheme by irradiation of helium ion

Succeeded forming self-assembled graphene nanoribbon on the twinned copper film

Graphene, Copper, Copper twin Scanning electron microscopical image
Scanning electron microscopical image

Graphene has high mobility and expected to apply to transistor channel. But, as graphene has no band gap, creating graphene nanoribbon which aims to form band gap is being tried mainly by top-down technique.

First time in the world, we have discovered that graphene nanoribbon will be formed on the thin twin copper on an elective basis. This nanoribbon is about 90mm width at minimum, but by controlling the width of twin copper a thinner nanoribbon can be obtained. Through bottom-up technique like we used this time, control of nanoribbon edge is hoped which is difficult by using top-down technique.

K. Hayashi, et al. J. Am. Chem. Soc., 134 , 12492 (2012)

2.2 CNT/graphene application to waste heat

Realized CNT dense growth for vertical wiring and heat waste base via

Microscopical image of CNT dense structure
Microscopical image of CNT dense structure

As CNT or grahpene has high heat conductivity, it is used as wiring material. They are also expected to use heat waste via to waste the heat generated in LSI. To waste the heat effectively lowering electric resistance of vertical wiring, it is needed to grow CNT densely in the hole punched on the base.

By optimizing catalyst and growth condition, we realized high density vertical growth which is ten times (1.4g/cm3) of existing CTN film.

Verified ReRAM low-current switching operation by using minute CNT electrode

ReRAM (Resistance Random Access Memory) is actively studied as new low-power-consumption memory using change of electrical resistance by force voltage during recent years. Smaller the electrode is, less the current flow becomes that means power consumption becomes also smaller. We verified switching operation (updating memory) with extreme low-current at pA level by using CNT of less than 10mm diameter as electrode.

ReRAM operation test of TiO2/Ti structure by CNT cantilever AFM
Probe radial dependence of set current related
Probe radial dependence of set current related

H. Nakano et al., Extended Abstracts of the 2011 International Conference on Solid State Devices and Materials, Nagoya, 2011, pp773-774

3.1 Development of low-voltage materials & process technique of phase-change film superlattice device

Appeared giant magnetoresistive effect from phase-change solid-state memory

We found that the giant magnetoresistive effect is developed from GeTe/SbTe superlattice, that is being studied as phase-change memory material, in despite of containing any magnetic material. On the magnetic field of 0.1 tesla (blue line) and no magnetic field (red and gray lines), current resistance changes 2000% at the room temperature. By using this effect, a brand-new type of low-power-consumption memory that can update existing hard disc and flash memory is likely of being materialized.

Appl. Phys. Lett. 99, 152105 (2011)
Copyright: American Institute of Physics