Programmable metallization cell

Last updated

The programmable metallization cell, or PMC, is a non-volatile computer memory developed at Arizona State University. PMC, a technology developed to replace the widely used flash memory, providing a combination of longer lifetimes, lower power, and better memory density. Infineon Technologies, who licensed the technology in 2004, refers to it as conductive-bridging RAM , or CBRAM. CBRAM became a registered trademark of Adesto Technologies in 2011. [1] NEC has a variant called "Nanobridge" and Sony calls their version "electrolytic memory".

Contents

Description

PMC is a two terminal resistive memory technology developed at Arizona State University. PMC is an electrochemical metallization memory that relies on redox reactions to form and dissolve a conductive filament. [2] The state of the device is determined by the resistance across the two terminals. The existence of a filament between the terminals produces a low resistance state (LRS) while the absence of a filament results in a high resistance state (HRS). A PMC device is made of two solid metal electrodes, one relatively inert (e.g., tungsten or nickel) the other electrochemically active (e.g., silver or copper), with a thin film of solid electrolyte between them. [3]

Device operation

The resistance state of a PMC is controlled by the formation (programming) or dissolution (erasing) of a metallic conductive filament between the two terminals of the cell. A formed filament is a fractal tree like structure.

Filament formation

PMC rely on the formation of a metallic conductive filament to transition to a low resistance state (LRS). The filament is created by applying a positive voltage bias (V) to the anode contact (active metal) while grounding the cathode contact (inert metal). The positive bias oxidizes the active metal (M):

M → M+ + e−

The applied bias generates an electric field between the two metal contacts. The ionized (oxidized) metal ions migrate along the electric field toward the cathode contact. At the cathode contact, the metal ions are reduced:

M+ + e− → M

As the active metal deposits on the cathode, the electric field increases between the anode and the deposit. The evolution of the local electric field (E) between the growing filament and the anode can be simplistically related to the following:

where d is the distance between the anode and the top of the growing filament. The filament will grow to connect to the anode within a few nanoseconds. [4] Metal ions will continue to be reduced at the filament until the voltage is removed, broadening the conductive filament and decreasing the resistance of the connection over time. Once the voltage is removed, the conductive filament will remain, leaving the device in a LRS.

The conductive filament may not be continuous, but a chain of electrodeposit islands or nanocrystals. [5] This is likely to prevail at low programming currents (less than 1 μ A) whereas higher programming current will lead to a mostly metallic conductor.

Filament dissolution

A PMC can be "erased" into a high resistance state (HRS) by applying a negative voltage bias to the anode. The redox process used to create the conductive filament is reversed and the metal ions migrate along the reversed electric field to reduce at the anode contact. With the filament removed, the PMC is analogous to parallel plate capacitor with a high resistance of several M Ω to G Ω between the contacts.

Device read

An individual PMC can be read by applying a small voltage across the cell. As long as the applied read voltage is less than both the programming and erasing voltage threshold, the direction of the bias is not significant.

Technology comparison

CBRAM vs. metal-oxide ReRAM

CBRAM differs from metal-oxide ReRAM in that for CBRAM metal ions dissolve readily in the material between the two electrodes, while for metal-oxides, the material between the electrodes requires a high electric field causing local damage akin to dielectric breakdown, producing a trail of conducting defects (sometimes called a "filament"). Hence for CBRAM, one electrode must provide the dissolving ions, while for metal-oxide RRAM, a one-time "forming" step is required to generate the local damage.

CBRAM vs. NAND Flash

The primary form of solid-state non-volatile memory in use is flash memory, which is finding use in most roles formerly filled by hard drives. Flash, however, has problems that led to many efforts to introduce products to replace it.

Flash is based on the floating gate concept, essentially a modified transistor. Conventional flash transistors have three connections, the source, drain and gate. The gate is the essential component of the transistor, controlling the resistance between the source and drain, and thereby acting as a switch. In the floating gate transistor, the gate is attached to a layer that traps electrons, leaving it switched on (or off) for extended periods of time. The floating gate can be re-written by passing a large current through the emitter-collector circuit.

It is this large current that is flash's primary drawback, and for a number of reasons. For one, each application of the current physically degrades the cell, such that the cell will eventually be unwritable. Write cycles on the order of 105 to 106 are typical, limiting flash applications to roles where constant writing is not common. The current also requires an external circuit to generate, using a system known as a charge pump. The pump requires a fairly lengthy charging process so that writing is much slower than reading; the pump also requires much more power. Flash is thus an "asymmetrical" system, much more so than conventional RAM or hard drives.

Another problem with flash is that the floating gate suffers leakage that slowly releases the charge. This is countered through the use of powerful surrounding insulators, but these require a certain physical size in order to be useful and also require a specific physical layout, which is different from the more typical CMOS layouts, which required several new fabrication techniques to be introduced. As flash scales rapidly downward in size the charge leakage increasingly becomes a problem, which led to predictions of its demise. However, massive market investment drove development of flash at rates in excess of Moore's Law, and semiconductor fabrication plants using 30 nm processes were brought online in late 2007.

In contrast to flash, PMC writes with relatively low power and at high speed. The speed is inversely related to the power applied (to a point, there are mechanical limits), so the performance can be tuned. [6]

PMC, in theory, can scale to sizes much smaller than flash, theoretically as small as a few ion widths wide. Copper ions are about 0.75 angstroms, [7] so line widths on the order of nanometers seem possible. PMC was promoted as simpler in layout than flash. [6]

History

PMC technology was developed by Michael Kozicki, professor of electrical engineering at Arizona State University in the 1990s. [8] [9] [10] [11] [12] [13] [14] Early experimental PMC systems were based on silver-doped germanium selenide glasses. Work turned to silver-doped germanium sulfide electrolytes and then to the copper-doped germanium sulfide electrolytes. [4] There has been renewed interest in silver-doped germanium selenide devices due to their high, high resistance state. Copper-doped silicon dioxide glass PMC would be compatible with the CMOS fabrication process.

In 1996, Axon Technologies was founded to commercialize the PMC technology. Micron Technology announced work with PMC in 2002. [15] Infineon followed in 2004. [16] PMC technology was licensed to Adesto Technologies by 2007. [6] infineon had spun off memory business to its Qimonda company, which in turn sold it to Adesto Technologies. A DARPA grant was awarded in 2010 for further research. [17]

In 2011, Adesto Technologies allied with the French company Altis Semiconductor for development and manufacturing of CBRAM. [18] In 2013, Adesto introduced a sample CBRAM product in which a 1 megabit part was promoted to replace EEPROM. [19]

NEC developed the so-called nanobridge technology, using Cu2S or tantalumpentoxide as dielectric material. Hereby copper (compatible with copper metallization of the IC) makes the copper to migrate through Cu2S or Ta2O5 making or breaking shorts between the copper and ruthenium electrodes. [20] [21] [22] [23]

The dominant use of this type of memory are space applications, since this type of memory is intrinsically radiation hard.

See also

Related Research Articles

<span class="mw-page-title-main">Anode</span> Electrode through which conventional current flows into a polarized electrical device

An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ACID, for "anode current into device". The direction of conventional current in a circuit is opposite to the direction of electron flow, so electrons flow from the anode of a galvanic cell, into an outside or external circuit connected to the cell. For example, the end of a household battery marked with a "+" is the cathode.

<span class="mw-page-title-main">Cathode</span> Electrode where reduction takes place

A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic cathode current departs also means that electrons flow into the device's cathode from the external circuit. For example, the end of a household battery marked with a + (plus) is the cathode.

<span class="mw-page-title-main">Electrochemistry</span> Branch of chemistry

Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically-conducting phase between electrodes separated by an ionically conducting and electronically insulating electrolyte.

<span class="mw-page-title-main">Electrode</span> Electrical conductor used to make contact with nonmetallic parts of a circuit

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit. Electrodes are essential parts of batteries that can consist of a variety of materials depending on the type of battery.

<span class="mw-page-title-main">Electrochemical cell</span> Electro-chemical device

An electrochemical cell is a device that generates electrical energy from chemical reactions. Electrical energy can also be applied to these cells to cause chemical reactions to occur. Electrochemical cells which generate an electric current are called voltaic or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells.

<span class="mw-page-title-main">Electroplating</span> Creation of protective or decorative metallic coating on other metal with electric current

Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be coated acts as the cathode of an electrolytic cell; the electrolyte is a solution of a salt of the metal to be coated; and the anode is usually either a block of that metal, or of some inert conductive material. The current is provided by an external power supply.

<span class="mw-page-title-main">Lithium-ion battery</span> Rechargeable battery type

A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. The negative electrode of a conventional lithium-ion cell is typically graphite, a form of carbon. This negative electrode is sometimes called the anode as it acts as an anode during discharge. The positive electrode is typically a metal oxide and is sometimes called the cathode as it acts as a cathode during discharge. Positive and negative electrodes remain positive and negative in normal use whether charging or discharging and therefore are clearer terms than anode and cathode, which are reversed during charging.

<span class="mw-page-title-main">Galvanic cell</span> Electrochemical device

A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous Oxidation-Reduction reactions. A common apparatus generally consists of two different metals, each immersed in separate beakers containing their respective metal ions in solution that are connected by a salt bridge or separated by a porous membrane.

<span class="mw-page-title-main">Electrolytic cell</span> Cell that uses electrical energy to drive a non-spontaneous redox reaction

An electrolytic cell is an electrochemical cell that utilizes an external source of electrical energy to force a chemical reaction that would otherwise not occur. The external energy source is a voltage applied between the cell′s two electrodes; an anode and a cathode, which are immersed in an electrolyte solution. This is in contrast to a galvanic cell, which itself is a source of electrical energy and the foundation of a battery. The net reaction taking place in a galvanic cell is a spontaneous reaction, i.e, the Gibbs free energy remains -ve, while the net reaction taking place in an electrolytic cell is the reverse of this spontaneous reaction, i.e, the Gibbs free energy is +ve.

<span class="mw-page-title-main">Gas-filled tube</span> Assembly of electrodes at either end of an insulated tube filled with gas

A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric discharge in gases, and operate by ionizing the gas with an applied voltage sufficient to cause electrical conduction by the underlying phenomena of the Townsend discharge. A gas-discharge lamp is an electric light using a gas-filled tube; these include fluorescent lamps, metal-halide lamps, sodium-vapor lamps, and neon lights. Specialized gas-filled tubes such as krytrons, thyratrons, and ignitrons are used as switching devices in electric devices.

A primary battery or primary cell is a battery that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell. In general, the electrochemical reaction occurring in the cell is not reversible, rendering the cell unrechargeable. As a primary cell is used, chemical reactions in the battery use up the chemicals that generate the power; when they are gone, the battery stops producing electricity. In contrast, in a secondary cell, the reaction can be reversed by running a current into the cell with a battery charger to recharge it, regenerating the chemical reactants. Primary cells are made in a range of standard sizes to power small household appliances such as flashlights and portable radios.

<span class="mw-page-title-main">Electric arc</span> Electrical breakdown of a gas that results in an ongoing electrical discharge

An electric arc is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma, which may produce visible light. An arc discharge is initiated either by thermionic emission or by field emission. After initiation, the arc relies on thermionic emission of electrons from the electrodes supporting the arc. An arc discharge is characterized by a lower voltage than a glow discharge. An archaic term is voltaic arc, as used in the phrase "voltaic arc lamp".

A polymer-based battery uses organic materials instead of bulk metals to form a battery. Currently accepted metal-based batteries pose many challenges due to limited resources, negative environmental impact, and the approaching limit of progress. Redox active polymers are attractive options for electrodes in batteries due to their synthetic availability, high-capacity, flexibility, light weight, low cost, and low toxicity. Recent studies have explored how to increase efficiency and reduce challenges to push polymeric active materials further towards practicality in batteries. Many types of polymers are being explored, including conductive, non-conductive, and radical polymers. Batteries with a combination of electrodes are easier to test and compare to current metal-based batteries, however batteries with both a polymer cathode and anode are also a current research focus. Polymer-based batteries, including metal/polymer electrode combinations, should be distinguished from metal-polymer batteries, such as a lithium polymer battery, which most often involve a polymeric electrolyte, as opposed to polymeric active materials.

<span class="mw-page-title-main">History of the battery</span> History of electricity source

Batteries provided the primary source of electricity before the development of electric generators and electrical grids around the end of the 19th century. Successive improvements in battery technology facilitated major electrical advances, from early scientific studies to the rise of telegraphs and telephones, eventually leading to portable computers, mobile phones, electric cars, and many other electrical devices.

Resistive random-access memory is a type of non-volatile (NV) random-access (RAM) computer memory that works by changing the resistance across a dielectric solid-state material, often referred to as a memristor.

<span class="mw-page-title-main">Supercapacitor</span> Electrochemical capacitor

A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor, with a capacitance value much higher than solid-state capacitors but with lower voltage limits. It bridges the gap between electrolytic capacitors and rechargeable batteries. It typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerates many more charge and discharge cycles than rechargeable batteries.

Research in lithium-ion batteries has produced many proposed refinements of lithium-ion batteries. Areas of research interest have focused on improving energy density, safety, rate capability, cycle durability, flexibility, and cost.

The glass battery is a type of solid-state battery. It uses a glass electrolyte and lithium or sodium metal electrodes. The battery was invented by John B. Goodenough, inventor of the lithium cobalt oxide and lithium iron phosphate electrode materials used in the lithium-ion battery (Li-ion), and Maria H. Braga, an associate professor at the University of Porto and a senior research fellow at Cockrell School of Engineering at The University of Texas.

<span class="mw-page-title-main">Adesto Technologies</span>

Adesto Technologies is an American corporation founded in 2006 and based in Santa Clara, California. The company provides application-specific semiconductors and embedded systems for the Internet of Things (IoT), and sells its products directly to original equipment manufacturers (OEMs) and original design manufacturers (ODMs) that manufacture products for its end customers. In 2020, Adesto was bought by Dialog Semiconductor.

Electrochemical Random-Access Memory (ECRAM) is a type of non-volatile memory (NVM) with multiple levels per cell (MLC) designed for deep learning analog acceleration. An ECRAM cell is a three-terminal device composed of a conductive channel, an insulating electrolyte, an ionic reservoir, and metal contacts. The resistance of the channel is modulated by ionic exchange at the interface between the channel and the electrolyte upon application of an electric field. The charge-transfer process allows both for state retention in the absence of applied power, and for programming of multiple distinct levels, both differentiating ECRAM operation from that of a field-effect transistor (FET). The write operation is deterministic and can result in symmetrical potentiation and depression, making ECRAM arrays attractive for acting as artificial synaptic weights in physical implementations of artificial neural networks (ANN). The technological challenges include open circuit potential (OCP) and semiconductor foundry compatibility associated with energy materials. Universities, government laboratories, and corporate research teams have contributed to the development of ECRAM for analog computing. Notably, Sandia National Laboratories designed a lithium-based cell inspired by solid-state battery materials, Stanford University built an organic proton-based cell, and International Business Machines (IBM) demonstrated in-memory selector-free parallel programming for a logistic regression task in an array of metal-oxide ECRAM designed for insertion in the back end of line (BEOL). In 2022, researchers at Massachusetts Institute of Technology built an inorganic, CMOS-compatible protonic technology that achieved near-ideal modulation characteristics using nanosecond fast pulses

References

  1. ↑ "Adesto Technologies Trademarks".
  2. ↑ Valov, Ilia; Waser, Rainer; Jameson, John; Kozicki, Michael (June 2011). "Electrochemical metallization memories-fundamentals, applications, prospects". Nanotechnology. 22 (25): 254003. Bibcode:2011Nanot..22y4003V. doi:10.1088/0957-4484/22/25/254003. PMID   21572191. S2CID   250920840.
  3. ↑ Michael N. Kozicki; Chakravarthy Gopalan; Murali Balakrishnan; Mira Park; Maria Mitkova (August 20, 2004). "Nonvolatile memory based on solid electrolytes" (PDF). Proceedings. 2004 IEEE Computational Systems Bioinformatics Conference. IEEE. pp. 10–17. doi:10.1109/NVMT.2004.1380792. ISBN   0-7803-8726-0. S2CID   2884270 . Retrieved April 13, 2017.
  4. 1 2 M.N. Kozicki; M. Balakrishnan; C. Gopalan; C. Ratnakumar; M. Mitkova (November 2005). "Programmable metallization cell memory based on Ag-Ge-S and Cu-Ge-S solid electrolytes". Symposium Non-Volatile Memory Technology 2005. IEEE. pp. 83–89. doi:10.1109/NVMT.2005.1541405. ISBN   0-7803-9408-9. S2CID   45696302.
  5. ↑ Muralikrishnan Balakrishnan; Sarath Chandran Puthen Thermadam; Maria Mitkova; Michael N. Kozicki (November 2006). "A Low Power Non-Volatile Memory Element Based on Copper in Deposited Silicon Oxide". 2006 7th Annual Non-Volatile Memory Technology Symposium. IEEE. pp. 111–115. doi:10.1109/NVMT.2006.378887. ISBN   0-7803-9738-X. S2CID   27573769.
  6. 1 2 3 Madrigal, Alexis (October 26, 2007). "Terabyte Thumb Drives Made Possible by Nanotech Memory". Wired . Archived from the original on May 11, 2008. Retrieved April 13, 2017.
  7. ↑ "Ion Sizes of Common Elements". Archived from the original on 2007-11-07., compare with Co
  8. ↑ "Programmable metallization cell structure and method of making same".
  9. ↑ "Programmable sub-surface aggregating metallization structure and method of making same".
  10. ↑ "Programmable microelectronic devices and method of forming and programming same".
  11. ↑ "Programmable conductor memory cell structure and method therefor".
  12. ↑ U.S. Patent 7,372,065
  13. ↑ "Programmable metallization cell structures including an oxide electrolyte, devices including the structure and method of forming same".
  14. ↑ B. Swaroop; W. C. West; G. Martinez; Michael N. Kozicki; L.A. Akers (May 1998). "Programmable current mode Hebbian learning neural network using programmable metallization cell". ISCAS '98. Proceedings of the 1998 IEEE International Symposium on Circuits and Systems (Cat. No.98CH36187). Vol. 3. IEEE. pp. 33–36. doi:10.1109/ISCAS.1998.703888. ISBN   0-7803-4455-3. S2CID   61167613.
  15. ↑ "Micron Technology Licenses Axon's Programmable Metallization Cell Technology". Press release. January 18, 2002.
  16. ↑ "Axon Technologies Corp. Announces Infineon as New Licensee of Programmable Metallization Cell Nonvolatile Memory Technology". Design And Reuse.
  17. ↑ "Adesto Technologies Wins DARPA Award to Develop Sub-Threshold Non-Volatile, Embedded CBRAM Memory". Press release. Adesto. November 29, 2010. Retrieved April 13, 2017.
  18. ↑ Altis et Adesto Technologies annoncent un partenariat sur les technologies Mémoires CBRAM avancées – Business Wire – published 27 June 2011 - viewed 28 March 2014 Archived 31 March 2014 at the Wayback Machine
  19. ↑ "Adesto's CBRAM targets 70 billion dollar market". Nanalyze. July 30, 2013. Retrieved April 13, 2017.
  20. ↑ Sakamoto, Toshitsugu; Banno, Naoki; Iguchi, Noriyuki; Kawaura, Hisao; Sunamura, Hiroshi; Fujieda, Shinji; Terabe, Kazuya; Hasegawa, Tsuyoshi; Aono, Masakazu (2007). "A Ta2O5 solid-electrolyte switch with improved reliability": 38–39. doi:10.1109/VLSIT.2007.4339718. S2CID   38195904.{{cite journal}}: Cite journal requires |journal= (help)
  21. ↑ "NEC: Nanobridge could build programmable ICs" . Retrieved 2020-10-22.
  22. ↑ "Low-power FPGA based on NanoBridge®technology" (PDF). Retrieved 2020-10-22.
  23. ↑ "Semiconductor device".
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.