Munehiro Tada

Polymer Solid-Electrolyte Switch Embedded on CMOS for Nonvolatile Crossbar Switch

A polymer solid-electrolyte (PSE) switch has been embedded in a 90-nm-node CMOS featuring a forming-less programming and extremely high on/off ratio of 105. A fast programming of 10 ns is also demonstrated for 50-nmΦ 1 k-b array by introducing the PSE switches integrated with a fully logic compatible process below 350°C. A high free volume in the PSE is supposed to result in the smooth formation of the Cu bridge without destroying the electrolyte, thereby also resulting in forming-less programming and high breakdown voltage. High disturbance reliability (T50; 50% fail) is extracted to be over 10 years at operation condition. The improved switching characteristics enable us to accurately program the crossbar circuit in a practical scale (32 × 32) without cell transistors. The developed switch is a strong candidate for realizing a low-power and low-cost nonvolatile programmable logic.

Low temperature (≤ 380°C) and high performance Ge CMOS technology with novel source/drain by metal-induced dopants activation and high-k/metal gate stack for monolithic 3D integration

We demonstrate high performance, 3D IC compatible, Ge n and p-MOSFETs fabricated at very low temperatures, below 380degC. The low temperature gate stack comprises of high-K/metal materials. Very low series resistance (2.23times10-4 Omega-cm at the lowest point of SRP) and shallow (92 nm) source/drain (S/D) junctions with high degree of dopant activation is achieved especially in n-MOSFETs using CMOS process compatible technique - metal (Co) induced dopant activation (Co MIDA) and Ge crystallization. Low S/D resistance in Ge n-MOSFETs has previously been highly challenging. The Ge n-MOSFET, fabricated at 360degC, has an electron mobility comparable to the highest one reported previously, while the Ge p-MOSFET shows a hole mobility higher than the universal Si mobility. The Ge n- and p-MOSFETs provide an excellent Ion/Ioff ratio ( ~1.1times103 for both). In addition to other uses, this low temperature Ge CMOS process serves as a compelling enabler for integrating high performance Ge transistors above metal layers as required by 3D-ICs without exceeding 400degC.

Programmable cell array using rewritable solid-electrolyte switch integrated in 90nm CMOS

Programmable devices such as SRAM-based FPGAs have the major challenges of power consumption and circuit area due to the excessive standby leakage current and the threshold voltage variation in highly scaled SRAM. Back-end-of-line (BEOL) device, which is integrated in the interconnect layers, is attractive for reducing the performance gap between FPGA and cell-based ASIC [1–4]. In this paper, we demonstrate the fundamental operations of a programmable cell array and a 32×32 crossbar switch using a nonvolatile and rewritable solid-electrolyte switch (nanobridge or NB). A 72% reduction in chip-area compared with that of a standard-cell-based design is achieved on a 90nm CMOS platform.

Chemical Structure Effects of Ring-Type Siloxane Precursors on Properties of Plasma-Polymerized Porous SiOCH Films

Physical and chemical properties of plasma-polymerized SiOCH films were investigated using ring-type siloxane monomers with several kinds of side-chain chemicals, and a design principle of the material and plasma-process was derived to obtain a porous SiOCH film of k < 2.5 with sub-nanometer-scaled porous structure framed by the original ring siloxane backbone. Here, the backbone siloxane structure is fixed as a six-membered Si-O ring of the 0.35 nmΦ, and no progen gas and no post-cure-process were utilized. It was found that unsaturated hydrocarbon side chains such as vinyl increase the deposition rate, and the original monomer structure tends to be kept, reducing the dielectric constant with the porous structure. Large alkyl groups increase the hydrocarbon content in the film as well as the deposition rate. The low radio-frequency power plasma with high precursor concentration also helps the original chemical structure to be preserved. The best solution is to use the ring-type siloxane with both of the vinyl (unsaturated hydrocarbon) and the large alkyl (saturated hydrocarbon) under the low-power plasma condition with the high partial pressure of the precursor. The plasma-polymerized porous SiOCH film is a strong candidate for the low-k film in scale-down 45/32 nm node ultralarge-scaled integrated interconnects featured by the simple and low-cost fabrication processes.

Improving Reliability of Copper Dual-Damascene Interconnects by Impurity Doping and Interface Strengthening

Electromigration (EM)-derived void nucleation and growth in 65-nm-node dual-damascene interconnects were investigated, and the effects of impurity doping as well as copper adhesion strength to a capping-dielectric layer (CAP) are clarified. It is found that surface-reductive treatment of the copper line improves its adhesion to the SiCN-CAP, elongating the incubation time of voiding at the via bottom. An aluminum doping is effective in suppressing both the void nucleation and growth. Consequently, an aluminum-doped copper alloy with the strong copper/CAP interface improves the EM lifetime by 50 times compared to that of a conventional pure copper. These results clearly indicate that blocking migration paths of vacancies through both grain boundaries and the copper/CAP interface is essential in improving the EM reliability.

High performance germanium N+∕P and P+∕N junction diodes formed at low Temperature (⩽380°C) using metal-induced dopant activation

We demonstrate high performance Ge N+∕P and P+∕N junction diodes at sub-380°C. Very low resistivity (2.2×10−4Ωcm) and shallow (92nm) junction with high degree of dopant activation are achieved especially in N+∕P junction formed at 360°C on Ge epitaxially grown on Si using complementary metal-oxide semiconductor process compatible-metal (Co) induced dopant activation technique. Excellent diode characteristics having ∼2×104 on/off ratio and high forward current density (221A∕cm2 for N+∕P and 135A∕cm2 for P+∕N at ∣VF∣=2V) are obtained in N+∕P and P+∕N junction diodes fabricated at 380°C on bulk Ge with a surface passivated layer [GeO2+low temperature chemical vopor deposition SiO2 (LTO)] isolation.

First demonstration of logic mapping on nonvolatile programmable cell using complementary atom switch

Reconfigurable nonvolatile programmable logic using complementary atom switch (CAS) is successfully demonstrated on a 65-nm-node test chip. Various logics are realized by synthesizing RTL codes and mapping the configurations into CAS-based programmable cell array. Each cell includes the two 4-input LUTs, 19×16 crossbar switch, and 368-b CAS. The CAS integrated over CMOS reduces the cell area by 78% compared to a conventional SRAM-based design.

Self-nucleation free and dimension dependent metal-induced lateral crystallization of amorphous germanium for single crystalline germanium growth on insulating substrate

In this work we have investigated Ni- or Au-induced crystallization and the lateral crystallization of planar amorphous germanium (α-Ge) on silicon dioxide at 360 °C without the deleterious effects of thermally induced self-nucleation. Subsequently, single crystalline Ge growth has been achieved on SiO2 by making dimension of α-Ge line to be smaller than the size of grains formed using Ni- and Au-induced lateral crystallizations at 360 °C. This method can be used to form the channel region of the MOS devices in upper layers of the three-dimensional integrated circuits at low temperatures.

Highly scalable nonvolatile TiOx/TaSiOy solid-electrolyte crossbar switch integrated in local interconnect for low power reconfigurable logic

A fully logic-compatible, nonvolatile crossbar switch using a novel dual-layer TiOx/TaSiOy solid-electrolyte, “NanoBridge”, has been developed for the first time, which is scalable to 50 nm and beyond and keeps the extremely low ON-resistance of ≪100 Ω. A key breakthrough is the dual-layer solid-electrolyte, in which TiOx works as an oxygen absorber as well as a superior ionic conductor, thus improving the yield, ON/OFF resistance ratio (≫106) and cycling endurance (≫103). The highly scalable 4 × 4 crossbar switch composed of NanoBridge integrated in a local Cu interconnect of a standard CMOS is successfully configured without select transistors. The nonvolatile solid-electrolyte, crossbar switch is a promising switch element for low power and low cost reconfigurable logic.

Improved Off-State Reliability of Nonvolatile Resistive Switch With Low Programming Voltage

A complementary atom switch (CAS) is proposed to realize low programming voltage and high off-state reliability for crossbar switch application. Two atom switches with bipolar operation are connected in series with opposite direction, in which the two atom switches work as a single element. The two off-state atom switches in the CAS complementarily divide voltage stress, greatly enlarging the off-state lifetime. The CAS is embedded in Cu BEOL on a 65-nm-node CMOS platform without degrading the CMOS and interconnect performances. The CAS using two atom switches is one of the candidates for realizing energy-efficient nonvolatile programmable switches.