Rao Feng

Germanium Nitride as a Buffer Layer for Phase Change Memory

The results of adhesion improvement and SET-RESET operation voltage reduction for the GeN buffer layer are presented. It is found that the adhesive strength between the Ge2Sb2Te5(GST) layer and the layer below could be increased at least 20 times, which is beneficial for solving the phase change material peeling issue in the fabrication process of phase change memory (PCM). Meanwhile, the RESET voltage of the PCM cell with a 3-nm-thick GeN buffer layer can be reduced from 3.5 V to 2.2 V. The GeN buffer layer will play an important role in high density and low power consumption PCM applications.

Si3.5Sb2Te3 Phase Change Material for Low-Power Phase Change Memory Application

Novel Si3.5Sb2Te3 phase change material for phase change memory is prepared by sputtering of Si and Sb2Te3 alloy targets. Crystalline Si3.5Sb2Te3 is a stable composite material consisting of amorphous Si and crystalline Sb2Te3, without separated Te phase. The thermally stable Si3.5Sb2Te3 material has data retention ability (10 years at 412K) better than that of the Ge2Sb2Te5 material (10 years at 383 K). Phase change memory device based on Si3.5Sb2Te3 is successfully fabricated, showing low power consumption. Up to 2.2 × 107 cycles of endurance have been achieved with a resistance ratio lager than 300.

Remarkable Resistance Change in Plasma Oxidized TiOx/TiNx Film for Memory Application

We report the experimental phenomenon of large resistance change in plasma oxidized TiOx/TiNx film fabricated on W bottom-electrode-contact (W-BEC) array. The W-BEC in diameter 260?nm is fabricated by a 0.18??m CMOS technology, and the TiOx/TiNx cell array is formed by rf magnetron sputtering and reactive ion etching. In current?voltage (I?V) measurement for current-sweeping mode, large snap-back of voltage is observed, which indicates that the sample changes from high-resistance state (HRS) to low-resistance state (LRS). In the I?V measurement for voltage-sweeping mode, large current collapse is observed, which indicates that the sample changes from LRS to HRS. The current difference between HRS and LRS is about two orders. The threshold current and voltage for the resistance change is about 5.0?10?5?A and 2.5?V, respectively. The pulse voltage can also change the resistance and the pulse time is as shorter as 30?ns for the resistance change. These properties of TiOx/TiNx film are comparable to that of conventional phase-change material, which makes it possible for RRAM application.

Study of phase change materials for phasechange random access memory

Phase change memory technology, which is regarded as one of the most promising candidates for the next generation non-volatile memory technology, has achieved rapid development in the past ten years. Meanwhile, related products based on this technology have been put into the market and mass production has come true. With the development of phase change memory technology, the fundamental research has become a hot topic in the fields of information, materials, and so on. Phase change storage medium based on chalcogenide is the basis and core of phase change memory. The performance of phase change memory is determined by phase change material’s performance. In this paper, the industrialization status of phase change memory are briefly introduced firstly, then the research progress of the commonly used GeSbTe phase change materials and the main phase transition mechanism is summarized. Finally, the C doping modification of the traditional GeSbTe and the phase change mechanism of C-doped GeSbTe materials is analyzed.

新型相变材料Ti 0.5 Sb 2 Te 3 刻蚀工艺及其机理研究

采用CF 4 和Ar混合气体研究了新型相变材料Ti 0.5 Sb 2 Te 3 (TST)的刻蚀特性, 重点优化和研究了刻蚀气体总流速、CF 4 /Ar的比例、压力和功率等工艺参数对刻蚀形貌的影响。结果表明, 当气体总流量为50 sccm、CF 4 浓度为26%﹑刻蚀功率为400 W和刻蚀压力为13.3 Pa时, 刻蚀速度达到126 nm/min, TST薄膜刻蚀图形侧壁平整而且垂直度好(接近90°)﹑刻蚀表面平整(RMS为0.82 nm)以及刻蚀的片内均匀性等都非常好。采用CF 4 和Ar混合气体研究了新型相变材料Ti 0.5 Sb 2 Te 3 (TST)的刻蚀特性, 重点优化和研究了刻蚀气体总流速、CF 4 /Ar的比例、压力和功率等工艺参数对刻蚀形貌的影响。结果表明, 当气体总流量为50 sccm、CF 4 浓度为26%﹑刻蚀功率为400 W和刻蚀压力为13.3 Pa时, 刻蚀速度达到126 nm/min, TST薄膜刻蚀图形侧壁平整而且垂直度好(接近90°)﹑刻蚀表面平整(RMS为0.82 nm)以及刻蚀的片内均匀性等都非常好。

An Improvement of the Thermal Stability of SnTe through Nitrogen Doping

Nitrogen doping is applied to improve the thermal stability of SnTe. The crystallization temperature Tc of SnTe is below room temperature, which can be elevated to 216°C by 7.65at.% nitrogen doping. Nitrogen doping results in the formation of SnNx in the nitrogen doped SnTe (N-SnTe) materials, which hinders the movement of atoms and suppresses the crystallization, leading to a better thermal stability. The crystallization activation energy (Ea) and data retention for ten years of 7.65at.% N-SnTe are 1.89eV and 81°C, respectively. Moreover, the voltage pulses have successfully triggered the SET and RESET operations of the N-SnTe based device at the voltage of 0.9 V and 2.6 V. The good thermal stability and reversible phase-change ability have proved the potential of N-SnTe for phase-change memory application.

Dry etching of new phase-change material Al1.3Sb3Te in CF4/Ar plasma

The dry etching characteristic of Al1.3Sb3Te film was investigated by using a CF4/Ar gas mixture. The experimental control parameters were gas flow rate into the chamber, CF4/Ar ratio, the O2 addition, the chamber background pressure, and the incident RF power applied to the lower electrode. The total flow rate was 50 sccm and the behavior of etch rate of Al1.3Sb3Te thin films was investigated as a function of the CF4/Ar ratio, the O2 addition, the chamber background pressure, and the incident RF power. Then the parameters were optimized. The fast etch rate was up to 70.8 nm/min and a smooth surface was achieved using optimized etching parameters of CF4 concentration of 4%, power of 300 W and pressure of 80 mTorr.