PCM Devices Research Articles

Recent Progress in Phase-ChangeMemory Technology

We survey progress in the PCM field over the past five years, ranging from large-scale PCM demonstrations to materials improvements for high–temperature retention and faster switching. Both materials and new cell designs that support lower-power switching are discussed, as well as higher reliability for long cycling endurance. Two paths towards higher density are discussed: through 3D integration by the combination of PCM and 3D-capable access devices, and through multiple bits per cell, by understanding and managing resistance drift caused by structural relaxation of the amorphous phase. We also briefly survey work in the nascent field of brain-inspired neuromorphic systems that use PCM to implement non-Von Neumann computing.

The Effect of Ti-Rich TiN Film on Thermal Stability of Ge2Sb2Te5 for Phase Change Memory

Investigation of the thermal stability of Ge2Sb2Te5 (GST) layer in contact with TiN film is very valuable for phase-change memory applications. In this work, the effect of Ti/N atomic ratio in TiN film on thermal stability of GST film has been thoroughly analyzed. After annealing at 410°C for 30 min, the Ti-rich TiN thin film is found to interact with GST material but there does not exist any mixing of Ti, Sb and Te atomic species at the interface between the stoichiometric TiN film and GST, which indicates the stoichiometric TiN film is stable against GST. A Ti-rich TiN film has Ti phase and other TiN compound phases. The presence of the Ti atoms promotes the mutual diffusion and interaction of Ti, Sb and Te under thermal annealing. To ensure the thermal stability of GST in contact with TiN and the performance of device, the Ti/N atomic ratio should be given more attention in the fabrication of PCM devices. Clear boundary and normal operation character are achieved in the T-shaped phase change memory devices with TiN0.6 film.

Efficient Management of PCM-based Swap Systems with a Small Page Size

Due to the recent advances in non-volatile memory technologies such as PCM, a new memory hierarchy of computer systems is expected to appear. In this paper, we explore the performance of PCM- based systems and discuss how this system can be managed efficiently. Specifically, we introduce three management techniques. First, we show that the page fault handling time can be reduced by attaching PCM on DIMM slots, thereby eliminating the software stack overhead of block I/O and the context switch time. Second, we show that it is effective to reduce the page size and turn off the read-ahead option under the PCM system where the page fault handling time is sufficiently small. Third, we show that the performance is not degraded even with a DRAM memory under a PCM device; this leads to the reduction of DRAM's energy consumption significantly compared to HDD-based systems. We expect that the result of this paper will lead to the transition of the legacy system structure of large memory - slow swap to a new paradigm of small memory - fast swap.

Localization of Joule Heating in Phase-Change Memory With Incorporated Nanostructures and Nanolayer for Reducing Reset Current

In this paper, we intensively investigated the proposed nanocontact phase-change memory (nano-C PCM) with incorporated nanostructures and high-resistivity nanolayer (nano-L) for reducing reset current. The high resistivity was able to be tuned by doping N into the conventional Ge2Sb2Te5 phase-change material. The analysis based on finite-element method exhibited that the current density in the nano-C PCM could be locally enhanced to about two times that of both conventional and nano-L PCM devices. This resulted in the localization of Joule heating in the nano-C PCM, making it have the highest temperature at the same programming current among the three types of PCM devices. Reset current of nano-C PCM could be greatly reduced to 8.2% of that of the conventional one, owing to its high-efficiency heating for amorphization.

Kinematic Analysis of Cpm Machine Supporting to Rehabilitation Process after Surgical Knee Arthroscopy and Arthroplasty

Abstract Existing commercial solutions of the CPM (Continuous Passive Motion) machines are described in the paper. Based on the analysis of existing solutions we present our conceptual solution to support the process of rehabilitation of the knee joint which is necessary after arthroscopic surgery. For a given novel structure we analyze and present proprietary algorithms and the computer application to simulate the operation of our PCM device. In addition, we suggest directions for further research.

Peculiarities of Bi doping of Ge–Sb–Te thin films for PCM devices

The influence of Bi doping on the thermal, electrical, and optical properties of Ge2Sb2Te5 thin films was investigated. The existence of two Bi concentration ranges with different influence of dopant on the properties of thin films was established. At low concentrations (0.5–1.0 wt.% of Bi), anomalous deviations of physical properties from monotonous concentration dependences were observed. This effect is explained by the use of percolation theory, where formation of infinite clusters is accompanied by critical phenomena at critical concentrations.

An analysis of heterotopic ossification in cervical disc arthroplasty: a novel morphologic classification of an ossified mass

Background contextAlthough the precise cause of heterotopic ossification (HO) remains unclear, it is certain that it increases with time. The reason why the reported occurrence rate has been given as a wider range is that there were no clinical reports that have addressed the occurrence rate based on the morphology and position. PurposeThe aim of this retrospective study was to determine whether radiological parameters had an influence on the formation of HO and to compare the results after cervical arthroplasty using Bryan (Medtronic Sofamor Danek, Memphis, TN, USA), PCM (Cervitech, Rockaway, NJ, USA), and Prestige LP (Medtronic Sofamor Danek) implants. Study design/settingA retrospective study. Patient sampleEighty-one patients were included. Outcome measurementThe occurrence of HO was determined at the four corners of the disc space according to the McAfee classification system. Heterotopic ossifications were classified into Type 1, Type 2, and Type 3 HOs (end plate, traction spur, and teardrop types) based on their morphologic features. The presence of preoperative ossifications, sex, type of device, operated level, hybrid implantation, depth behind the prosthesis, cervical lordotic angle, and segmental angle between the footplates of the prosthesis were assessed as predictors in terms of location and morphologic features. MethodsEighty-one patients after 95 cervical arthroplasties using the Bryan (35 segments), PCM (30 segments), and Prestige LP implants (30 segments) underwent postoperative radiographs or three-dimensional computed tomography with a mean follow-up period of 46, 39, and 30 months, respectively, after the operation. ResultsThe overall incidence of all cases and one-level subgroup were 64.2% and 60.3%, respectively. According to the types of device, the incidence of HO was 49% (Bryan), 80% (PCM), and 60% (Prestige). Type 1 HO (62.1%) was found only in the posterosuperior disc space. Type 2 HO (13.7%) was primarily detected in the anterosuperior disc space rather than the posterosuperior disc space (3.2%). Type 3 HO (4.2%) developed only in the anterior disc space. In the anterior disc space, the incidence of Type 2 and Type 3 HOs was highest in the PCM group. In the posterior disc space, the Bryan group showed a lower proportion in the high McAfee class than the other device groups. The occurrence of Type 1 HO in the posterosuperior disc space was significantly related with the presence of preoperative ossification (p=.030), ossification in the ligamentum nuchae (p=.027), male sex (p=.042), and PCM device (p=.012). A well-fitting (p<.002) and less lordotic segmental angle (p<.015) were correlated with Type 1 HO. Implantation in the upper cervical level (p=.016) and hybrid implantation with cage (p=.033) or artificial disc (p=.048) on the upper adjacent level were significant risk factors for anterior Type 2 HO. Cervical lordotic angle at 1 month after surgery had a significant connection with the occurrence of anterior Type 2 HO in both groups of all cases (p=.032) and one-level subgroup (p=.000). ConclusionsType 1 HO developed mostly in the posterior disc space. Type 2 HO was the dominant type in the anterior disc space. Type 3 HO developed only in the anterior disc space. It is certain that both Type 1 and Type 2 HOs are related to biomechanical stresses (compressive force for Type 1 HO and traction force for Type 2 HO). It is suggested that a cervical arthroplasty should be selected in terms of the implant level, hybrid conditions on the upper adjacent segment, disc design vulnerable to the pseudotranslation, the presence of preoperative ossification, and fitting implants to end plates to reduce the development of HO.

Delta-compressed caching for overcoming the write bandwidth limitation of hybrid main memory

Limited PCM write bandwidth is a critical obstacle to achieve good performance from hybrid DRAM/PCM memory systems. The write bandwidth is severely restricted in PCM devices, which harms application performance. Indeed, as we show, it is more important to reduce PCM write traffic than to reduce PCM read latency for application performance. To reduce the number of PCM writes, we propose a DRAM cache organization that employs compression. A new delta compression technique for modified data is used to achieve a large compression ratio. Our approach can selectively and predictively apply compression to improve its efficiency and performance. Our approach is designed to facilitate adoption in existing main memory compression frameworks. We describe an instance of how to incorporate delta compression in IBM's MXT memory compression architecture when used for DRAM cache in a hybrid main memory. For fourteen representative memory-intensive workloads, on average, our delta compression technique reduces the number of PCM writes by 54.3%, and improves IPC performance by 24.4%.

Understanding Phase Change Memory Reliability and Scaling by Physical Models of the Amorphous Chalcogenide Phase

AbstractPhase change memory (PCM) devices are based on the electrically-induced change of phase within an active chalcogenide material. PCM features large resistance window, fast threshold/phase switching and high endurance, thus motivating a broad interest as potential Flash replacement and/or nonvolatile storage class memory. Despite the relatively mature progress of research and technology, there is still a wide debate about the ultimate scaling perspective for PCMs. Structural relaxation, crystallization and noise affecting the amorphous chalcogenide phase need to be addressed by accurate physical models for a realistic scaling projection. This work discusses the scaling of PCM devices in terms of the conduction mechanisms and structural stability of the amorphous chalcogenide phase. Resistance window narrowing, current fluctuations, resistance drift and crystallization in the amorphous phase will be explained by a unified model for thermal excitation of the structure by many-phonon phenomena. The downscaling of the reset current, needed to reduce the cell area in memory arrays, and thermal disturb between adjacent cells during reset will be finally addressed to assess the scaling capability of high-density PCM crossbar architectures.

Magnetic Resonance Imaging Clarity of the Bryan®, Prodisc-C®, Prestige LP®, and PCM® Cervical Arthroplasty Devices

Prospective, randomized, controlled and double-blinded study on imaging of artificial discs. The purpose of this study is to compare postoperative imaging characteristics of the 4 currently available cervical arthroplasty devices at the level of implantation and at adjacent levels. Cervical arthroplasty is being performed increasingly frequently for degenerative disc disease and, in most cases, with frank neural compression. Unlike lumbar arthroplasty, performed mainly for axial back pain, decompression of neural elements may need to be confirmed with postoperative imaging after cervical arthroplasty. Preoperative and postoperative magnetic resonance imaging scans of 20 patients who had undergone cervical arthroplasty were assessed for imaging quality. Five cases each of the Bryan (Medtronic Sofamor Danek, Memphis, TN), Prodisc-C (Synthes Spine, Paoli, PA), Prestige LP (Medtronic Sofamor Danek), and PCM devices (Cervitech, Rockaway, NJ) were analyzed. Six blinded spinal surgeons scored twice sagittal and axial T2-weighted images using the Jarvik 4-point scale. Statistical analysis was performed comparing quality before surgery and after disc implantation at the operated and adjacent levels and between implant types. RESULTS.: Moderate intraobserver and interobserver reliability was noted. Preoperative images of patients in all implant groups had high-quality images at operative and adjacent levels. The Bryan and Prestige LP devices allowed satisfactory visualization of the canal, exit foramina, cord, and adjacent levels after arthroplasty. Visualization was significantly impaired in all PCM and Prodisc-C cases at the operated level in both the spinal canal and neural foramina. At the adjacent levels, image quality was statistically poorer in the PCM and Prodisc-C than those of Prestige LP or Bryan. CONCLUSIONS.: Postoperative visualization of neural structures and adjacent levels after cervical arthroplasty is variable among current available devices. Devices containing nontitanium metals (cobalt-chrome-molybdenum alloys in the PCM and Prodisc-C) prevent accurate postoperative assessment with magnetic resonance imaging at the surgical and adjacent levels. Titanium devices, with or without polyethylene (Bryan disc or Prestige LP), allow for satisfactory monitoring of the adjacent and operated levels. This information is crucial for any surgeon who wishes to assess adequacy of neural decompression and where monitoring of adjacent levels is desired.