|Computer memory types|
|Early stage NVRAM|
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.NEC has a variant called "Nanobridge" and Sony calls their version "electrolytic memory".
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.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.
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.
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):
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:
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.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.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.
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.
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.
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.
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.
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,so line widths on the order of nanometers seem possible. PMC was promoted as simpler in layout than flash.
PMC technology was developed by Michael Kozicki, professor of electrical engineering at Arizona State University in the 1990s.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. 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.Infineon followed in 2004. PMC technology was licensed to Adesto Technologies by 2007. 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.
In 2011, Adesto Technologies allied with the French company Altis Semiconductor for development and manufacturing of CBRAM.In 2013, Adesto introduced a sample CBRAM product in which a 1 megabit part was promoted to replace EEPROM.
An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical 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 out the anode into the outside circuit. In a galvanic cell, the anode is the electrode at which the oxidation reaction occurs.
Cathode rays are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode. They were first observed in 1869 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.
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.
An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic cells or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells. A common example of a galvanic cell is a standard 1.5 volt cell meant for consumer use. A battery consists of one or more cells, connected in parallel, series or series-and-parallel pattern.
In chemistry and manufacturing, electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential.
Electroplating is a process that uses an electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode. The term is also used for electrical oxidation of anions on to a solid substrate, as in the formation of silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is primarily used to change the surface properties of an object, but may also be used to build up thickness on undersized parts or to form objects by electroforming.
The Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell. The Hall–Héroult process applied at industrial scale happens at 940–980°C and produces 99.5–99.8% pure aluminium. Recycled aluminum requires no electrolysis, thus it does not end up in this process.
A lithium-ion battery or Li-ion battery is a type of rechargeable battery. Lithium-ion batteries are commonly used for portable electronics and electric vehicles and are growing in popularity for military and aerospace applications. A prototype Li-ion battery was developed by Akira Yoshino in 1985, based on earlier research by John Goodenough, Stanley Whittingham, Rachid Yazami and Koichi Mizushima during the 1970s–1980s, and then a commercial Li-ion battery was developed by a Sony and Asahi Kasei team led by Yoshio Nishi in 1991.
A regenerative fuel cell or reverse fuel cell (RFC) is a fuel cell run in reverse mode, which consumes electricity and chemical B to produce chemical A. By definition, the process of any fuel cell could be reversed. However, a given device is usually optimized for operating in one mode and may not be built in such a way that it can be operated backwards. Standard fuel cells operated backwards generally do not make very efficient systems unless they are purpose-built to do so as with high-pressure electrolysers, regenerative fuel cells, solid-oxide electrolyser cells and unitized regenerative fuel cells.
A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte.
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.
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. This technology bears some similarities to conductive-bridging RAM (CBRAM), and phase-change memory (PCM).
A nanowire battery uses nanowires to increase the surface area of one or both of its electrodes. Some designs, variations of the lithium-ion battery have been announced, although none are commercially available. All of the concepts replace the traditional graphite anode and could improve battery performance.
A lithium-ion capacitor (LIC) is a hybrid type of capacitor classified as a type of supercapacitor. Activated carbon is typically used as the cathode. The anode of the LIC consists of carbon material which is pre-doped with lithium ions. This pre-doping process lowers the potential of the anode and allows a relatively high output voltage compared with other supercapacitors.
The thin film lithium-ion battery is a form of solid-state battery. Its development is motivated by the prospect of combining the advantages of solid-state batteries with the advantages of thin-film manufacturing processes.
Electrodeionization (EDI) is a water treatment technology that utilizes electricity, ion exchange membranes and resin to deionize water and separate dissolved ions (impurities) from water. It differs from other water purification technologies in that it is done without the use of chemical treatments and is usually a polishing treatment to reverse osmosis (RO). There are also EDI units that are often referred to as continuous electrodeionization (CEDI) since the electric current regenerates the resin mass continuously. CEDI technique can achieve very high purity, with conductivity below 0.1 μS/cm.
A polymer capacitor, or more accurately a polymer electrolytic capacitor, is an electrolytic capacitor (e-cap) with a solid electrolyte of a conductive polymer. There are four different types:
The sodium-ion battery (NIB) is a type of rechargeable battery analogous to the lithium-ion battery but using sodium ions (Na+) as the charge carriers. Its working principle and cell construction are identical with that of the commercially widespread lithium-ion battery with the only difference being that the lithium compounds are swapped with sodium compounds: in essence, it consists of a cathode based on a sodium containing material, an anode (not necessarily a sodium-based material) and a liquid electrolyte containing dissociated sodium salts in polar protic or aprotic solvents. During charging, Na+ are extracted from the cathode and inserted into the anode while the electrons travel through the external circuit; during discharging, the reverse process occurs where the Na+ are extracted from the anode and re-inserted in the cathode with the electrons travelling through the external circuit doing useful work. Ideally, the anode and cathode materials should be able to withstand repeated cycles of sodium storage without degradation.
Research in lithium-ion batteries has produced many proposed refinements of lithium-ion batteries. Areas on research interest have focused on improving energy density, safety, rate capability, cycle durability, flexibility, and cost.
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.