Hideto Hidaka

A high-density and high-speed 1T-4MTJ MRAM with Voltage Offset Self-Reference Sensing Scheme

A high-density and high-speed memory cell named 1-transistor 4-magnetic tunnel junction (1T-4MTJ) has been proposed for magnetic random access memory (MRAM). The new 1T-4MTJ cell has been successfully demonstrated by a 1 Mb MRAM test device, using a 130 nm CMOS process. The sensing scheme of a self-reference sense amplifier with Voltage offset (SRSV) enables high-speed memory operation (access time) of tAC=56 nsec and 50 MHz@4cycle.

Evolution of embedded flash memory technology for MCU

Embedded flash memory technology has undergone tremendous growth of demands with various performance requirements driven by expanded applications of MCU (Micro Controller Unit) products. High temperature operations with highest reliability for auto-motive applications, very low power embedded EEPROM functions for smart-cards, and ultra low-voltage operations for medical applications are driving factors in developing embedded flash technologies. Together with evolving memory cell technology, resolving performance/power trade-offs by developing dedicated design platforms with optimized eFlash technology, memory interface & bus designs, and the whole chip design methodologies, has realized advanced MCU products line-ups by split-gate MONOS flash technology with a wide range of applied products including auto-motive and security applications.

Value creation in SOC/MCU applications by embedded non-volatile memory evolutions

Flash-MCU, micro-controller with embedded flash memory storage (eFlash), has seen a tremendous up-surge in real-time control application markets, with assumed 15-20% CAGR. The programmable code storage provided by eFlash contributes to production cost reduction and real-time adaptive control applications, realizing a value innovation with remarkable cost/value advantage. The diversified advanced eFlash technology for converging flash-MCU products challenges new market drivers like automotive and smart-IC cards. Current status and future directions of flash-MCU with evolution of LSI by programmability functions are also reviewed.

7.3 A 28nm embedded SG-MONOS flash macro for automotive achieving 200MHz read operation and 2.0MB/S write throughput at T i , of 170°C

Accelerated advances in automotive technology, such as sophisticated real-time engine controls for higher fuel efficiency and advanced driver-assistance systems (ADAS), are expanding the application range of Flash MCUs, microcontrollers with embedded Flash memory (eFlash). In addition to consistent demands for faster random access, shorter rewrite time and larger memory capacity in eFlash, there are increasingly intense requirements for robust operations and high data reliability under extremely high junction temperature (Ti,) of 170°C. On the other hand, along with device scaling beyond 40nm generation, the reliability of eFlash systems is constrained by not only eFlash memory cells but also peripheral transistors and metal interconnections. As oxide films in transistor devices and between metal interconnections are getting thinner, their time-dependent dielectric breakdown (TDDB) lifetime is critically degraded, which poses a great challenge in advanced eFlash design. This paper presents 28nm eFlash macros for automotive with four key features. The first feature is a 28nm split-gate (SG)-MONOS cell array with temperature-adjusted overdrive wordline (WL) voltage control to realize both 200MHz random access and more than 10× longer TDDB lifetime of WL drivers. Second, we implement a high-voltage control technique to relax electrical stress on memory cells and peripheral devices by temperature-adaptive step pulse erase control (TASPEC). Third, we achieve high write throughput of 2.0MB/s by source-side injection (SSI) programming with negative back-bias achieving 63% reduction of program pulse time. Finally, we reduce RF noise by 19dB with a spread-spectrum phase-shifted clock-generation technique for over-the-air program updates while achieving a high write throughput.

7.6 A 90nm embedded 1T-MONOS flash macro for automotive applications with 0.07mJ/8kB rewrite energy and endurance over 100M cycles under Tj of 175°C

The computerization of automotive control has expanded the application range of micro controller units (MCUs). A high-end engine-control unit (ECU) requires high-performance Flash MCUs, which integrate high-speed CMOS logic and large high-performance embedded Flash memories (eFlash) [1,2]. There are also broad markets for motor control MCUs: used to control actuators in parts such as seats, windows, and mirrors. In order to integrate analog circuits to control the high voltage (HV) drivers in these parts, those MCUs have been manufactured in Flashless process, and external EEPROM chips are being used. EEPROM chips work as “learning memories” which store the calibration data to optimize analog circuit performance in the field. Replacement of external EEPROM chips by eFlash, resulting in less additional process cost and higher rewrite endurance, is a requirement for more elaborate learning at a higher data sampling rate. In addition to automotive grade reliability under extremely harsh temperature conditions, low power consumption is also a strong requirement as the number of MCUs used in motor control systems is increasing.

Embedded Magnetic RAM

In Chapter 7, magnetic RAM (MRAM) technology is introduced as a key technology candidate for creating new applications such as nonvolatile RAM. After an introduction of the history and basic principles of MRAM, we look into MRAM technology and basic design as well as on various memory cell architectures in Section 7.1. Then overviews on representative MRAM design examples, possible applications, and future challenges of MRAM are provided in Section 7.2. Finally nonvolatile memory frontiers and challenges are discussed in Section 7.3 as a conclusion of Chapters 6 and 7. The focus of this chapter is to highlight and summarize important concepts of the new technology.

Embedded flash technology for automotive applications

Higher fuel-efficient engine and advanced driver assistance system (ADAS) require the further progress of embedded Flash (eFlash) technology for the automotive microcontroller units (MCUs). Continuous evolution of eFlash has satisfied the automotive requirements for the excellent reliability with the lower failure ratio of single ppm level and the high performance under harsh operating condition. Especially our unique spilt-gate MONOS (SG-MONOS) has been leading the worlds first most cutting-edge eFlash for automotive MCUs since 90nm process node and has been already scaled down to 28nm one, because of its excellent reliability and process scalability. In addition our gate polished structure for the low-profile SG-MONOS enables to implement high performance and power efficient high-K metal gate (HKMG) CMOS transistors, while the conventional stacked floating gate Flash can be hardly applied. As the convergence candidate of eFlash for automotive Flash MCUs, SG-MONOS can contribute to the realization of the future worlds leading green vehicles and autonomous-driving era.

Embedded Flash Memory

Chapter 6 first introduces the expanding variety of applications and requirements for embedded nonvolatile memory especially in microcontroller applications, then describes how and why embedded flash memory has expanded the functions and applications supported by process, device, and circuit technology evolutions. Embedded-specific flash memory technologies focused on the floating-gate and charge-trapping devices with split-gate and 2Tr cell concepts are overviewed in Section 6.2. Descriptions on basic embedded flash design concepts and examples of actual embedded flash designs along with challenges and future targets for embedded flash memory are provided in Section 6.3.

A 1Mb High-Density Toggle-MRAM with Symmetrical Read/Write Operations

A high-density MRAM cell structure, 1T-4MTJ cell is successfully applied to a Toggle-mode MRAM, with reduced effective cell array size and symmetrical Read/Write operations. A lMb-lT-4MTJ Toggle MRAM with 66 MHz operation (tAC = 43.4 nsec) is demonstrated.

Applications and Technology Trend in Embedded Flash Memory

Chapter 2 first introduces the history of the micro-controller unit (MCU) with significant growth of the market by on-chip flash-memory innovation affecting the whole supply chain from development of hardware and software, to production, inventory control, and lifetime maintenance. Then described are how and why embedded flash memory has expanded functions and applications by finding new embedded uses supported by device, circuit, and sub-system designs followed by expanding variety of applications and requirements by automotive and smart-card applications. Finally embedded flash technology prospects partly leading to the necessity of emerging non-volatile memory development are overviewed.