Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
  • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
  • G11C13/0021—Auxiliary circuits
  • G11C13/004—Reading or sensing circuits or methods
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
  • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
  • G11C13/0009—RRAM elements whose operation depends upon chemical change
  • G11C13/0011—RRAM elements whose operation depends upon chemical change comprising conductive bridging RAM [CBRAM] or programming metallization cells [PMCs]
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
  • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
  • G11C13/0021—Auxiliary circuits
  • G11C13/0069—Writing or programming circuits or methods
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
  • H10N70/20—Multistable switching devices, e.g. memristors
  • H10N70/24—Multistable switching devices, e.g. memristors based on migration or redistribution of ionic species, e.g. anions, vacancies
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
  • H10N70/801—Constructional details of multistable switching devices
  • H10N70/841—Electrodes
  • H10N70/8416—Electrodes adapted for supplying ionic species
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
  • H10N70/801—Constructional details of multistable switching devices
  • H10N70/881—Switching materials
  • H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
  • H10N70/8822—Sulfides, e.g. CuS
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
  • H10N70/801—Constructional details of multistable switching devices
  • H10N70/881—Switching materials
  • H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
  • H10N70/8825—Selenides, e.g. GeSe
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
  • H10N70/801—Constructional details of multistable switching devices
  • H10N70/881—Switching materials
  • H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
  • H10N70/8828—Tellurides, e.g. GeSbTe
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
  • H10N70/801—Constructional details of multistable switching devices
  • H10N70/881—Switching materials
  • H10N70/884—Switching materials based on at least one element of group IIIA, IVA or VA, e.g. elemental or compound semiconductors
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
  • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
  • G11C13/0021—Auxiliary circuits
  • G11C13/004—Reading or sensing circuits or methods
  • G11C2013/0047—Read destroying or disturbing the data
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
  • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
  • G11C13/0021—Auxiliary circuits
  • G11C13/004—Reading or sensing circuits or methods
  • G11C2013/0052—Read process characterized by the shape, e.g. form, length, amplitude of the read pulse
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
  • G11C2213/30—Resistive cell, memory material aspects
  • G11C2213/33—Material including silicon
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
  • G11C2213/50—Resistive cell structure aspects
  • G11C2213/52—Structure characterized by the electrode material, shape, etc.

Definitions

• the invention relates to a method for reading a resistive memory cell and a resistive memory cell for carrying out the method.
• Resistive memory elements from an antiserial circuit of two resistive memory cells combine the fast access time of DRAM main memory with the non-volatility of flash memory and are therefore suitable for combining main memory and mass memory in computer technology.
• digital information is encoded in two stable states 0 and 1, in which the memory element has a high total resistance in each case.
• German patent 10 2011 012 738 discloses designing resistive memory elements such that they have different capacitances in states 0 and 1, and non-destructively detecting this difference during readout. The disadvantage of this advantage must be paid that the usable signal in an array of many memory elements decreases rapidly with increasing array size.
• a method of reading out a resistive memory cell having two electrodes spaced from each other by an ionically conductive resistive material is achieved by applying a write voltage from a stable high resistance state (HRS) to a stable lower resistance state low resistance state (LRS).
• the method requires a memory cell in which the writing voltage drives migration of ions through the ion-conducting resistive material and an electrically conductive path is formed through the ion-conducting resistive material along the way of this migration.
• HRS stable high resistance state
• LRS stable lower resistance state low resistance state
• the ionically conductive resistive material may be ionically conductive only and electronically isolated. It may be electronic but also, for example, a semiconductor. From the electronic conductivity, the resistance values of HRS and LRS and in particular the usable stroke between these resistance values depend. The material may in particular be a solid electrolyte. The ionic conductivity is needed for the migrations of the ions forming the electrically conductive path.
• the ions may, for example, be ions of the material of an electrode. This is then referred to as an "electrochemical metallization" memory cell (ECM), but the ions can also be driven, for example, by oxygen ions of the ion-conducting resistive material through the ion-conducting resistive material, which is referred to as a valence change-mechanism memory cell (VCM).
• ECM electrochemical metallization memory cell
• VCM valence change-mechanism memory cell
• the read voltage is applied as a read pulse, wherein the number of ions driven through the ion-conducting resistive material during the pulse is higher than the height and duration of the pulse is adjusted to be from the state to form an electrically conductive path through the ionically conductive resistive material at least until onset of current flow through that path, and thus for transition to a reduced state VRS Resistance value and a predetermined relaxation time for the return to the state HRS sufficient, but not for the transition to the state LRS.
• the formation of the electrically-conductive path in the transition from the HRS state to the LRS state is a gradual process, the speed and progress of which are determined by the supply of ions driven through the ion-conductive resistive material.
• the formation and the stability of the electrically conductive path can be precisely metered via the number of ions which are driven through the ion-conducting resistive material.
• the path Starting from the higher resistance state, as the number of ions transported increases, the path progresses from one electrode to the other electrode, until tunneling occurs as the first contact allowing current to flow through the path.
• the current flow through this tunnel junction depends exponentially on the width of the tunnel barrier. If this width changes by only one atomic diameter, the tunneling current already changes by three orders of magnitude.
• the stability of the tunneling contact thus depends crucially on how many atoms the tunnel current is carried. If there is an atom in contact, over which substantially all of the tunneling current flows, it virtually collapses if it diffuses away an atom or is removed from the tunnel junction by another thermally or chemically induced process. So just as many ions have been driven through the ion-conducting resistive material that a tunneling contact has just come into existence, this is highly unstable. If further ions are driven, the initially fragile tunnel junction is removed. The tunneling current spreads to more atoms by making the path, especially the top of the path, wider and thicker. At the same time, the tunneling barrier of the ion-conducting resistive material becomes smaller as the path progresses further towards the other electrode.
• the read pulse is terminated while the electrically conductive path contains a tunnel barrier.
• the memory cell If the memory cell is already in the LRS state before the start of the read pulse, its resistance value does not change. If, on the other hand, it is in the HRS state before the start of the read pulse, an electrically conductive path is formed by the ion-conducting resistive material which is only metastable and after a relaxation time which can be set by the duration and duration of the pulse, ie by the number of ions driven from the end of the reading pulse disintegrates by itself.
• the read pulse thus causes a brief transition to a metastable third state with a reduced resistance value (VRS), but is again in the original state HRS with a high resistance value after the predetermined relaxation time has elapsed.
• VRS reduced resistance value
• the VRS can thus be used to read out the memory cell in such a way that during read-out it has in any case a resistance value which is lower than the state HRS and still maintains its original state (LRS or HRS) after completion of the read-out.
• the readout according to the invention is therefore non-destructive.
• This functionality is also called a "selector.”
• a pulse can be made from the write pulse to the read pulse by reducing its magnitude from a write pulse by shortening its duration versus a write pulse, or by applying a combination of both measures is advantageous to shorten the duration of the read pulse, since the reading then works faster and also in the drive circuit no additional voltage level for the read pulse is required.
• the resistance value in the metastable state VRS can be the same resistance value which also sets in the stable state LRS. Both states can then still be non-destructively distinguished from one another in an advantageous embodiment of the invention, for example by measuring the resistance value with another pulse at the end of the relaxation time, the magnitude and duration of which are selected such that it is not suitable for a transition from HRS to VRS still for a transition from LRS to HRS enough. If the memory cell was in the HRS state before the first pulse, the first pulse has placed it in the VRS state, which has disappeared after the relaxation time has elapsed. The second pulse thus again registers a high resistance value. On the other hand, if the memory cell was in the LRS state before the first pulse, it is still present for a long time and therefore after the relaxation time has elapsed. The second pulse thus registers a low resistance value.
• a state VRS is selected whose resistance value lies between the resistance values of the states HRS and LRS. Then, a current measurement during a single read pulse is sufficient to uniquely determine whether the memory cell was in HRS state or LRS state before the beginning of the pulse.
• the resistance value of the VRS state is determined by the interplay of the specific configuration (materials and geometry) of the memory cell with the duration and magnitude of the read pulse.
• the relaxation time of the state VRS should be at least so long that the switching to this state also after many transitions from HRS to VRS and back, or after many write operations between HRS and LRS, each causing a slight degradation of the ion-conducting resistive material, still works reliably. On the other hand, it determines the working speed when reading the memory cell. As an advantageous compromise relaxation times have been found in the range between 10 ns and 10. It has also proved to be advantageous if the intended storage duration for the storage cell is at least 1000 times as long as the relaxation time.
• a memory cell is selected, which can be converted by a second writing voltage with reverse polarity from the stable state LRS in the stable state HRS.
• the memory cell may in particular be a bipolar switching memory cell, the magnitude of which is a smaller
• a transient condition VRS only intervenes on the way from HRS to LRS, but usually not in the opposite direction from LRS to HRS. For this purpose, it would be necessary to break up the electrically conductive path just enough so that it recovers itself after a relaxation time has elapsed.
• the thermally activated processes basically drive the system into the state of greater entropy and work to destroy the order in the presence of the electrically conductive path. Therefore, the formation of a useful transient intermediate state on the way from HRS to LRS is preferable to the formation of such a state on the way from LRS to HRS.
• a memory cell is selected, which is in antiserial series connection with a further memory cell.
• the read pulse is applied via the series connection.
• a memory element designed as a resistive double cell can be selected according to German Patent 10 2009 023 153.
• Such a memory element has two distinguishable states 0 and 1, which are encoded in the state combinations HRS / LRS or LRS / HRS. In both states, the memory element has a high resistance value, so that in an array of many memory elements, each parasitic current path is interrupted by non-addressed memory elements at at least one location. As a result, individual memory elements can be read even in large arrays with a sufficiently strong signal.
• the first memory cell is converted by the read pulse in the state VRS, while the second memory cell remains in the state LRS.
• the state combination VRS / LRS with a reduced resistance value is thus present, so that a clearly detectable read current flows.
• the first memory cell After expiration of the relaxation time, the first memory cell returns to the state HRS again, so that the original state combination HRS / LRS is restored.
• the memory element If the memory element is in the LRS / HRS state before the read pulse, neither of the two memory cells is switched, since in each case one polarity would be required which is opposite to that of the read pulse. Thus, the memory element remains in a high resistance state, and the read pulse drives only a very small current through the memory element.
• the readout method according to the invention utilizes the significantly larger jump in the resistance value which is experienced by each memory cell of the memory element during the transition between the states HRS and LRS.
• This jump can be in the order of magnitude 10 6 to 10 8 .
• the resulting read current is much larger than the parasitic current through the non-addressed memory elements connected in parallel on the same bitline.
• the readout method according to the invention thus has the effect that a non-destructive readout of the memory element no longer has to be paid for by a drastic reduction of the usable array size.
• a relaxation time of 10 seconds or less is chosen. This represents the area in which the return to the state HRS or the remaining in the state LRS is still practically controllable.
• the goal of the development of resistive memory is a universal memory that unites the formerly separate working and mass storage devices.
• Relaxation times in the claimed range occur, for example, for resistance values of the state LRS between 10 kQ and 15 kQ, preferably between 12.5 kQ and 13.5 kQ, in particular for resistance values around 12.9 kQ, in which the state VRS of one or a few atoms in a tunnel contact is worn.
• a high resistance value of the state VRS is accompanied by a short relaxation time, while, conversely, a low resistance value is associated with a long relaxation time.
• the exact context is material- and condition-specific.
• the invention therefore also relates to a memory cell for carrying out the method according to the invention.
• the memory cell comprises two electrodes and a resistive memory material connected between the electrodes, which has a stable state LRS with a lower electrical resistance and a stable state HRS with a higher electrical resistance.
• the memory material can be converted into a third metastable state VRS whose resistance value is at most one tenth of the resistance value of the HRS state, the memory material changing into the HRS state on the basis of this state VRS after a predetermined relaxation time has elapsed.
• the storage material itself can be changed for conversion into the metastable state, for example by driving oxygen ions of the storage material through the storage material to form an electrically conductive path.
• ions of the material of one of the electrodes may be driven by the storage material.
• the prior art undesirable state VRS can be made to be technically safe from the HRS state by the claimed distance of its resistance value from that of the HRS state.
• an antiserial circuit of two such memory cells to form a memory element can thereby be made nondestructive, without this diminishing the possibility of realizing large arrays of these memory elements.
• the memory material is an ion-conducting resistive material, through which an electrically conductive path runs between the two electrodes in the state LRS.
• such a path is formed gradually so that, starting from the HRS state, it can be controlled, in particular by the magnitude and duration of an electrical pulse applied to the memory cell, whether the state VRS or the state LRS is reached.
• the resistance value of the state VRS may correspond to that of the state LRS.
• the state LRS By waiting for the relaxation time is still distinguishable from the state LRS. If the state has returned to the HRS state after the relaxation time has elapsed, it was the VRS; If it persists even after the relaxation time has elapsed, it is the stable state LRS. As a rule, however, the resistance of the VRS state will be higher than the resistance of the LRS state due to the instability of the VRS state.
• the resistance value of the state VRS is at least twice as high, preferably at least five times as high and very particularly preferably at least ten times as high as the resistance value of the state LRS. Then these two states can be distinguished technically safe before the relaxation time expires.
• the resistance value of the state VRS is between 10 kQ and 15 kQ, preferably between 12.5 kQ and 13.5 kQ.
• a state VRS which returns to the state HRS with relaxation times on the order of current DRAM access times, can be implemented particularly easily with an ion-conducting resistive material as memory material, through which an unstable electrically conductive path runs between the two electrodes.
• Such a path is particularly unstable if the contact between the path and at least one of the electrodes only consists of one or a few parallel tunnel paths or even only of a contact-forming atom.
• one atom has the quantum conductivity e 2 / h and the resistance value 12.9 kQ.
• the resistance value of the state LRS is 5 k ⁇ or less, preferably 2 k ⁇ or less, and most preferably 1 k ⁇ or less.
• the storage material is an ion-conducting resistive material which is electrochemically metallized by at least one electrode material when switching from the HRS state to the LRS state.
• the physical and chemical forces acting resolutely on an electrically conductive path are particularly large, so that short relaxation times can be achieved.
• high electromotive forces (EMF) form a strong driving force for dissolution processes in these storage materials.
• the memory material may contain a semiconductor and at least one of the electrodes may contain a noble metal.
• the storage element then goes into the state LRS (or VRS) in that the semiconductor reacts with the noble metal to form an electrically conductive path through the storage element.
• the semiconductor may be germanium or silicon, for example, and the noble metal may be, for example, silver.
• the memory material contains a compound of the semiconductor with sulfur, selenium or tellurium.
• the compound may be germanium sulfide (GeS x ) or germanium selenide (GeSe x ). be.
• the stoichiometry of this compound can then be used to determine how much the semiconductor is bound in the compound and what amount of substance of the semiconductor is available for the formation of the electrically conductive path.
• a similar effect can be achieved with a memory material containing a compound of at least one metal which is also contained in at least one electrode.
• the metal may in particular be copper or silver, and the compound may contain as further element in particular sulfur, selenium or tellurium.
• the compound may be Ag x S, Cu x S, Ag x Se, Cu x Se or Cu x Te.
• Figure 1 Time course of voltage and current during readout according to two exemplary embodiments (partial images a and b) of the method according to the invention.
• Figure 1 illustrates the non-destructive readout of a resistive memory element of two memory cells A and B with the inventive method.
• the read pulse R differs from the write pulse W with the same polarity due to its lower height, but lasts just as long as the write pulse W.
• the read pulse R differs from the write pulse W with the same polarity due to its shorter duration but just as high.
• the time curve of the voltage U (U over time t) applied to the storage element is plotted in the upper curve
• the time curve of the current I (I over time t) driven by the storage element is plotted in the lower curve.
• the states in which the memory cells A and B, which are connected in series in the memory element, are indicated in each case in FIGS. 1 a and 1 b.
• the memory element is poled so that positive read or write voltages can transfer the memory cell A from the state HRS to VRS or LRS.
• the memory element is in the state LRS / HRS (0).
• a positive read pulse (step 1) does not change anything in this state, so that the total resistance of the memory element remains high and no appreciable current is driven through the memory element.
• a negative write pulse (step 2) switches the memory element to the state HRS / LRS (1). It remains high impedance, so that still no appreciable current flows. If a positive read pulse is applied again (step 3), the memory cell A is switched from HRS to VRS, and the total resistance of the memory element decreases. It flows a well detectable read current.
• step 4 the memory element is permanently transferred to the state LRS / HRS (0) by a positive write pulse.

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• 2013
  • 2013-12-11 DE DE102013020517.4A patent/DE102013020517B4/de not_active Expired - Fee Related
• 2014
  • 2014-10-29 EP EP14828126.4A patent/EP3080482A1/de not_active Withdrawn
  • 2014-10-29 CN CN201480066846.3A patent/CN105980743B/zh not_active Expired - Fee Related
  • 2014-10-29 WO PCT/DE2014/000551 patent/WO2015085977A1/de active Application Filing
  • 2014-10-29 JP JP2016538608A patent/JP2017505504A/ja not_active Ceased
  • 2014-10-29 US US15/039,217 patent/US9865343B2/en not_active Expired - Fee Related

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