JP2010516053A - Electrical switching element - Google Patents

Abstract

  The switching element 10 includes a first layer 14 and a second layer 22, and the switching element has a first state and a second state, and in the first state, the first layer 14 And the second layer 22 are stacked in the contact region 22, and in the second state, the first layer and the second layer are peeled off in the contact region 22, and the switching element applies a switching stimulus to the switching element. Thus, the first state is switched to the second state irreversibly.

Description

  The present invention relates to a switching element for irreversibly switching between a first state and a second state.

  The invention further relates to a device incorporating such an electrical element.

  There is an ongoing effort for development that is cheap and easy to use write-once-read-many storage. While such a device can be programmed once, it can be read many times. A well-known example is a programmable read only memory (PROM) on a regular compact disk or electrical device. All such devices require switching elements that can be switched once but read multiple times.

  An example of such a switching element is disclosed in US 2004/0149552, a document relating to a US patent application. The disclosed device comprises an electronic switch used as an electronic memory element having a conductive organic polymer layer sandwiched between and in contact with two metal conductive elements. In the initial post-manufacturing state, the organic polymer is relatively highly conductive, and the post-manufacturing state functions to represent, for example, binary bits 0 or 1, depending on the coding convention used. Configure a first state of the possible memory elements. A relatively high voltage pulse can be applied between the two metal conductive elements, resulting in a significant reduction in the current carrying capacity of the organic polymer. The change in current carrying capacity of the organic polymer layer is generally irreversible and constitutes a second stable state of the memory element that can be used to encode other binary bits 1 or 0. In the disclosed example, the organic conductive layer comprises a commercially available polyethylenedioxythiophene: polystyrene sulphonic acid (PSS). With PEDOT: PSS, the decrease in conductivity after a high voltage pulse is between 2 and 3 orders of magnitude.

  The selection of this PEDOT: PSS material has the disadvantage that many device parameters are interrelated, such as conductivity in both states and the switching voltage to be applied. Because all of these depend on the same material. This hinders the proper design of the switching element with respect to the design specification relationship for devices that require the switching element.

  Accordingly, a first object of the present invention is to provide a switching element that improves the degree of design freedom and a device incorporating the element.

  The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

  According to the present invention, during switching of the switching element, the change of the state of the switch, that is, the change from the first state to the second state is performed in such a form that the first layer is peeled off from the second layer. It is based on the insight that it is done advantageously by causing a change in the physical integrity of Such delamination can be accomplished by supplying a compound that provides a gas species when the switching signal is applied so that the generated gas pushes away the first and second layers in the contact area, either or both of the first and second layers. It is realized by supplying to. Stacking here is to be interpreted as meaning that there is a certain interaction between the first layer and the second layer in the contact region in the first state before switching. That means. This can be, for example, adhesive molecular force. In addition, delamination is from such that the first and / or second layer can be collapsed as a fuse or partially removed from the switching element as in an explosive device, and the present switching mechanism and It is also what distinguishes the devices.

  A compound that provides a gas species by switching should be taken to mean, for example, a compound that vaporizes or chemically reacts so as to release the gas species but not cause any kind of explosion. Thus, the present invention is advantageous for situations where, for example, an array with dense switching elements is used in a memory and / or where the integrity of the device is critical. The chemical reaction includes a photochemical reaction or a heat induction reaction that becomes a gas releasing compound.

  The present invention is advantageous over the prior art because switching is based on a change in the physical integrity of the device rather than the need to change the properties of the first layer and / or the second layer. is there.

  The switching process according to the present invention includes a self-limiting process. Such a process is advantageous because it provides highly reliable and controllable switching.

  Such a switching stimulus can be an electrical signal, a radiation signal or a heating signal.

  In a preferred embodiment, the switching stimulus has an electronic signal.

  In a first variant of this embodiment, the electrical signal can drive a heating element that generates heat to vaporize the compound. The heating element can be provided by either the first or second layer. This is advantageous in such a case, since it is effective at least in the area where vaporization is performed on the contact surface in the contact area and gas is required accordingly. In other alternatives, the electrical signal can result in a direct chemical reaction of the compound, such as in electrolysis or decomposition. This is advantageous in this case because no heat is required. Electrolysis is advantageous because it occurs at relatively low voltages. A preferred example of a compound that can be conveniently electrolyzed at low voltages is water.

  In an embodiment, the switching stimulus has radiation. This allows, for example, contactless switching of the device using, for example, visible or UV light. In such a case, the switching element is optically switched. In one variation, the radiation heats the vaporizing compound to cause delamination. However, if heating is not preferred, an advantageous variant is used in which the compound is chemically reacted so that the radiation releases a gas as in a photochemical reaction.

  In an embodiment, at least a part of the contact surface is located in a cavity in the support layer. When the contact area is encapsulated, it is possible to sufficiently prevent the gas species necessary for peeling from diffusing into the periphery of the contact area without exhibiting the peeling effect. The effect of the support layer depends on its gas permeability, the lower it is, the better the layer provides its function. The support layer may be made of a material having an appropriate gas permeability. This can be organic such as a photoresist or inorganic such as in silicon dioxide.

  In an embodiment, the switching element is an electrical switch whose first state represents a first electrical state and whose second state represents a second electrical state. An electrical state means a state of electrical resistance, electrical capacitance and / or electrical induction or a mixture thereof. Thus, delamination will induce an increase in electrical resistance measured over the contact area from the first layer to the second layer. Similarly, such delamination induces a space between the first layer and the second layer, so that the capacitance of the contact area as measured across the contact area is changed by switching. . This embodiment is advantageous when the switching element has to function as an electrical element, for example to connect or disconnect different circuit parts of the device. It may also function as a fuse. Furthermore, it can be advantageously used as a write-once electrical memory element if the reading of its contents can be done electrically by detecting a change in electrical state. Note that switching may be performed as necessary as described above.

  In a preferred embodiment, the first layer and the second layer are electrically conductive. Resistive switching elements are preferred because the resistance can be easily detected in the memory. One of the layers can be an electrode layer. In such a case, the metal is preferably made of a metal because it is relatively impermeable to gas. This is advantageous for reasons that will become apparent with respect to the support layer herein.

  In an embodiment, at least one of the first layer and the second layer has another compound, and the other compound is a conductive compound.

  Preferably, the resistance of the layer is determined by another compound that is different from the compound capable of supplying the gas species. In that case, the compound selects the conductivity of the first state according to the degree of freedom in design and the characteristics of other compounds independent of the switching conditions depending mainly on the compound capable of supplying the gas species. Those that provide the opportunity can be independently selected.

  In the embodiment, the switching element has a mirror layer, and this mirror layer has the first shape in the first state of the switching element and the first shape in the second state of the switch. Having a different second shape. Here, the mirror layer means a layer that reflects radiation. This is advantageous because it allows detection of the state of the switch by using radiation that is non-contact and separate from, for example, an electrical switching mechanism (and thus without interference). The mirror layer can be one of the first and second layers so that deformation of the first and / or second layer due to the delamination results in deformation of the mirror layer. It is not necessary to provide sufficient conversion through the switching device. This mirror layer is preferably made of metal, so that a feasible electrode layer can advantageously function as a mirror layer.

  In an embodiment, the device comprises a switching element according to claim 5 for electrically disconnecting two parts of the device.

  In an embodiment, the device comprises a switching element according to claim 8, which switching element provides a switchable mirror.

  In an embodiment, the apparatus comprises a switching device according to claim 1, wherein the switching element is a memory element for storing information.

  2006 Nature 441 or unpublished international application IB 2006/052510 discloses a capacitive device with a PEDOT / PSS electrode used to contact the gold electrode in the cavity. Between the gold and the PEDOT / PSS layer is a self-assembled system or monolayer where the device constitutes a capacitor or molecular junction.

These and other aspects of the invention will be described in more detail with reference to the following drawings.
Sectional drawing which shows the 1st Example of the switching apparatus of this invention. The plot of the current-voltage of a switching apparatus. The plot of the current-time of a switching apparatus. The top view of the switching apparatus before switching in ambient conditions. The top view of the switching apparatus after switching in ambient conditions. The figure which shows the scanning electron microscope image of the cross section of the switching apparatus after supply of a switching signal.

FIG. 1 shows a schematic sectional view of a first embodiment of the switching element of the present invention. This figure is not drawn to scale. The switching element 10 is formed on a substrate 12, a silicon wafer having a diameter of 4 inches (10 cm) in this example. The substrate 12 in this example is passivated with a thermally grown layer of silicon oxide (not shown). However, this layer is not essential to the present invention. The gold electrode 14 used thermal evaporation of chromium or titanium having a thickness of 1 nm followed by gold having a thickness of 40 nm, positive photoresist (HPR504 ^™ ), mask-defined exposure of the photoresist, and redundant gold etching. It is formed by standard photolithography patterning. The substrate is then cleaned with fuming nitric acid and then rinsed with deionized water.

Thereafter, an electrically insulating layer 16 is applied on top of the substrate that also covers the gold electrode. A cavity 18 is defined in the insulating layer 16 above the gold electrode 14 so that the gold electrode is exposed over the contact area 20. In this example, a 500 nm thick negative photoresist (ma_N 1407 ^TM or L6000.5 ^TM ) is used as the insulating layer 16 patterned by standard processing according to specifications. Thus, the silicon substrate is provided with a plurality of cavities each having a circular contact area with a diameter in the range of 1 to 50 microns.

Prior to supplying the intermediate layer 22 to the substrate to fill such a cavity, the contact area is first cleaned by exposure to UV ozone or O ₂ plasma, followed by a reduction such as an ethanol bath or N ₂ / O ₂ plasma. Steps are made. In this example, the intermediate layer is poly (3,4-ethylenedioxythiophene) and polystyrene in water as supplied by HC Starck AG mixed with a few drops of surfactant (FSO100 ^™ (DuPont)). A 100-200 nm thick layer of a conductive polymer composition with sulfone (poly (3,4-ethylenedioxythiophene) and polystyrenesulphonic; PEDOT / PSS) is spin coated and the film is dried in vacuum at room temperature for 1 hour. Formed by. This film generally has a conductivity of 1 S / cm.

The second electrode 24 is provided on the top of the PEDOT / PSS film. And in this example, a 100 nm thick gold layer is deposited or sputtered so that after patterning the gold electrode is removed from the substrate at all points except where it must remain after the etching. It is configured using a photolithography process using a 500 nm thick layer of a positive photoresist (HPR504 ^™ ) to be formed. The gold second electrode 24 is etched using sputter etching, after which the PEDOT / PSS layer 22 is etched using STS RIE etching with O ₂ plasma using the gold second electrode as a mask. Etched.

  In the test switching element, the electrodes 14 and 24 are connected to bond pads located near the cavity when the substrate is viewed from the top so that contact of the switching element, for example using a probe station, does not collapse the cavity. To be patterned. FIG. 3A shows an SEM image of the assembled switching element. A circular area 25 represents the contour of the cavity of the switching element.

  The current-voltage characteristics (IV) of switching elements with different contact areas are maintained under ambient conditions by connecting their first and second electrodes to a power source and raising the bias from 0 to 5V. Measured. To illustrate such switching, FIG. 2A shows, by way of example, a portion of the current-voltage characteristic 26 of a switching element having a contact area with a diameter of 50 microns. Up to a bias of 1V, the device behaves like a linear resistance, but at a bias above 1V, the resistance begins to increase slowly at first and finally increases very rapidly by a factor of five. This increase in resistance is reversible. Furthermore, the second record of the switching element shows that the element continues to behave as a linear resistor but with a different resistance. Thus, the first low resistance defines the first state of the switching element, and the second high resistance defines the second state of the switching element.

  Such switching is also evident from the current transient (It) 28 of FIG. 2B where there is a similar element recording as used for IV26 recording by subjecting the switching element to a 2V block pulse. In this case, a resistance change of four orders of magnitude is induced to separate the first and second states of the switching element. Therefore, by using a switching voltage of only 2V, the element can be conveniently switched.

  2A and 2B also show IV30 and It32, respectively, recording switching elements similar to those used to record IV26 and It28 while maintaining the element in a vacuum. Switching is not observed. Also, It34, which has element recording at 140 ° C., does not exhibit switching. The current remains constant over at least 10 seconds over a long period of time.

  The switching voltage is independent of the size of the contact area within the contact area described here.

  FIG. 3A shows an image of the switching element before switching, and FIG. 3B shows the result after switching. Such a result is typical for all of the switched switching elements. The electrode 24 in the region on the top of the cavity leading to 25 has been pushed upwards to be deformed into a spherical or spherical shape.

  4A and 4B show images of the cross-section of the switching element after switching, and it can be seen that the PEDOT / PSS layer 22 has peeled from the gold electrode 14 to form an interstitial space or space 36 therebetween. .

The switching mechanism is as follows. At voltages generally higher than 2V, water is electrolyzed to provide the gaseous species H ₂ and / or O ₂ that cause such exfoliation. Although using a mixture as described above, spin coating of PEDOT / PSS with added dimethyl sulfoxide generally improves the conductivity of the PEDOT / PSS layer by a factor of 100 and reduces the switching voltage to approximately 1V. Has been observed. This is advantageous for the application of the switching element in a device that allows exclusively low voltages.

  Therefore, the device according to this embodiment is in contrast to the prior art document on increased resistance change with significantly lower switching voltage due to advantageous switching as shown in the document US 2004/0149552 A1 in the US patent application. Is advantageous. Independent optimization of the switching parameters and switching state parameters of the device.

  The described embodiments can be differentiated with respect to materials and geometrical arrangements without departing from the invention.

  Thus, the geometric device configuration can be changed. The electrode 24 may cover the layer 22 so that the entire layer 22 is provided within the cavity and between the electrodes 14 and 24. Layer 22 may be entirely within the cavity, and its surface in contact with electrode 24 may also be within the cavity. It will be apparent that the shape and depth of such cavities can be varied appropriately.

  The substrate can be any conceivable substrate.

  Layer 16 can be formed of different materials. Advantageous is a material that provides low gas permeability to keep the gas condensed at the contact surface. Other suitable organic materials can also be used. In addition, an inorganic material such as silicon dioxide or silicon nitride can be used. This promotes integration in the semiconductor device. If the device is an electrical switch, layer 16 is preferably electrically insulating. However, if the switching element is not an electrical switching element, this need not be the case.

  The PEDOT / PSS layer need not be patterned. In the example described above, the current through the device is forced through the contact region 20 because the layer 16 is insulative. Thus, the gas forming layer is limited within the diameter of the cavity.

  The conductivity of the intermediate layer 22 can be changed by choosing different materials for the layer. Thus, in an alternative embodiment, layer 22 does not have a conductor such as PEDOT / PSS, but does have a semiconductor or a material that has a lower conductivity than that of the semiconductor. This material may be organic or inorganic. In this embodiment, by selecting materials with different electrical conductivity, the resistance of the first state of the switching device can be changed without having to change the dimensions (cavity diameter) of the switching device. This is advantageous for circuit configurations where the future size is a predefined parameter.

  The material of layer 22 is most preferably a polymer that produces conductivity as a result of the interaction of impurities (dopants) with a conductive polymer, such as a polymer material, particularly with conductive groups therein. good. Examples of these materials include polyaniline, polythiophene, polyacetylene, polypyrrole, etc. that can be replaced by side groups such as alkoxy, alkyl, aryl and the like. Alternatively, the contact layer material can be a material that incorporates a conductive element such as an epoxy or other polymer filled with silver, graphite or the like. However, these latter materials are clearly less preferred in that the uniformity of the layer is quite small and the uniformity of the element over its surface area is reduced.

Most preferably, poly- (3,4-substituted thiophene) is used as the conductive polymer. The best known example of this class of polymers is by 3,4-alkylenedioxy substitution, often referred to as PEDOT. The alkylene group is preferably an optionally substituted C ₁ -C ₄ -alkylene group, preferably here a C ₁ to C ₁₂ -alkyl- or phenyl substituted methylene group, optionally C ₁ to It is selected from the group consisting of C ₁₂ -alkyl- or phenyl substituted 1,2-ethylene groups, 1,3-propylene groups and 1,2-cyclohexylene groups. Additives may be added to increase conductivity and processing effects such as surfactants.

  If the gas supply mechanism relies on electrolysis of a compound such as water present in a current carrying medium such as PEDOT / PSS, replace the PEDOT / PSS for other compounds such as polyaniline By changing the conductivity of layer 22 by means of which the resistance of the first state of the switching device voltage required to allow a certain critical current to pass through the device to switch the device can be controlled. . Higher conductivity means lower switching voltage. There will be a region where the voltage drop in the layer is very low, so that the switching voltage is almost independent of the conductivity, in which the resistance of the first state of the device is the switching It can be adjusted as needed by selecting the appropriate material for the layer 22 without changing the voltage.

  In one embodiment, an apparatus according to what has been described herein is provided in which the intermediate layer 22 is polyvinyl alcohol (PVA) having a low conductivity. This PVA layer is spin coated from a 5 weight percent solution of hydrolyzed 87-89% PVA (Aldrich) in water to a layer thickness of 100 to 200 nm. This layer is dried at room temperature for 1 hour. The conductivity of the PVA layer is much lower than that of PEDOT / PSS. Thus, the first state of the switching device is very high. In the IV curve, the current increases from a nanoampere level at low voltage to a microampere at approximately 80V when the device switches.

  Other compounds that supply gas species for switching can also be used in the apparatus according to the invention. Thus, for example, this can be a volatile compound. Alternatively, the compound is sensitive to heat as a result of a chemical reaction that proceeds in the process of supplying the gas species. In these cases, the electrode 14 that is advantageously used as a resistive heater is thus given a high resistance that generates sufficient heat for vapor deposition. Advantageously, this deposition is carried out approximately at the contact surface where it is desired to peel off. This embodiment provides a switching circuit that does not use the second electrode 24. Thus, this is at least partially decoupled from the electrical circuit for measuring the resistance that would use the electrodes 14 and 24 to sample the state of the switch. Heating can also be performed by irradiation, for example, as with a laser.

  In addition, it is possible to use a compound that releases a gas by a photochemical reaction.

  Several methods can be used for the deposition of layer 22. Such deposition methods will often depend on the material used for the layer. Some deposition methods advantageously allow in situ patterning, such as inkjet printing. Thus, individual patterning of layer 22 is not necessary. In other variations, layer 22 is not patterned at all.

  Suitable materials for the first and / or second electrodes include gold, copper, conductive oxide, aluminum, doped silicon GaAs, other III-V semiconductors, mercury, nickel, platinum, palladium, etc. . The adhesion of the layer 22 to the electrode is used in an advantageous manner to match the adhesion of the electrode layer to the intermediate layer. The stronger the adhesion, the more difficult it is to peel, which makes switching more difficult.

  In order to adjust the adhesion between the first layer and the second layer, the bonding may be adjusted using a monomolecular layer having an appropriate chemical composition.

  A self-assembling system may be applied to the cavity between the first layer 14 and the second layer 22 to adjust the adhesion between these layers. This self-assembled layer may have one or more monolayers. In the case of a gold electrode, a monomolecular layer such as alkanethiol or alkanedithiol can be used. However, it should be understood that the type of system used will depend on the layers requiring adhesion and the degree of adhesion required. Monolayers can be applied according to processing as described in the non-published international application IB2006 / 052510.

  The bond can be a chemical bond or a physical bond as revealed in the unpublished application.

  In the described embodiment, the first electrode 14 can function as a mirror. In that case, the switching device provides a switchable mirror. Because, in the first state of the switch, the mirror surface is almost flat before switching, while in the second state after switching, the mirror has a spherical shape as shown in FIGS. 3A and 3B. It is because it presents. An alternative variant has the second electrode 24 and / or the intermediate layer 22 as the mirror. If the mirror layer is a buried layer, such as layer 22, the surrounding or covering layer, such as 16 and / or 14 and / or 24, is detected using the radiation that the mirror is to reflect by the mirror. It is preferable to provide such a transparent window.

  A switchable mirror can be used to cause a change in the reflected illumination beam. That is, the state of the switch can be detected using radiation-based principles and systems. Thereby, the switching device can provide an optical memory function, for example. One skilled in the art will know how to provide such a detection system.

  It should be noted that the detection of the state of the switch can include radiation-based detection such as light detection as described herein above, but the switching of the device need not necessarily be stimulated by a radiation signal.

  Thus, the switch can be switched electrically, for example, according to the principles of the present invention. Alternatively, the switch may be switched using illumination to conveniently decouple switching from detection.

  Preferably, the manufacture of electrical elements constitutes a step in the manufacture of electronic devices. Such an electronic device may have a plurality of electrical elements as configured according to the present invention, and more preferably other passive and active elements. The elements of the present invention can also be integrated in an array as shown, thereby enabling the manufacture of memory. Each switching element including the electrode is electrically connected in series with a selection device such as a diode or a transistor between the word line and the bit line by a known technique. If the electronic device is an integrated circuit, it is assumed that it is suitable to integrate the elements of the invention in an interconnect structure, or it is more appropriate to make such integration on top of the passivation layer. It is assumed. It should be appreciated that the first and second electrodes are suitably provided as part of a layer in which other patterns such as interconnects, electrodes, bond pads, etc. are defined. This is produced appropriately at the plate level, after which the individual devices are separated from one another. A person skilled in the art knows how to integrate the element into an electronic device and use the advantageous properties of the switching element to use the element as a switch in memory or other means. It is a spear.

  The above-described embodiments are illustrative rather than limiting the present invention, and those skilled in the art can configure many alternative embodiments without departing from the scope of the appended claims. It is a spear. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The singular representation of an element or product does not exclude the presence of a plurality of such elements or products. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be utilized.

Claims (11)

  A switching element including a first layer and a second layer and having a first state and a second state, wherein in the first state, the first layer and the second layer are in contact with each other In the second state, the first layer and the second layer are peeled off in the contact region, and the switching element is applied to the switching element by applying a switching stimulus to the switching element. A switching element that switches irreversibly from the state to the second state.   The switching element according to claim 1, wherein the switching stimulus comprises an electrical signal.   The switching element according to claim 1, wherein the switching stimulus comprises radiation.   The switching element according to claim 1, wherein at least a portion of the contact surface is positioned in a cavity in the support layer.   The switching element according to claim 1, wherein the switching element is an electrical switch having a first state representing a first electrical state and a second state representing a second electrical state.   6. The switching element according to claim 5, wherein at least one of the first layer and the second layer is conductive.   The switching element according to claim 6, wherein at least one of the first layer and the second layer includes another compound, and the other compound is a conductive compound. element.   2. The switching element according to claim 1, further comprising a mirror layer, wherein the mirror layer has a first shape in the first state of the switching element and the first state in the second state of the switch. A switching element having a second shape different from the shape.   6. A device comprising the switching element according to claim 5, wherein the device electrically disconnects two parts of the device.   9. A device comprising a switching element according to claim 8, wherein the switching element provides a switchable mirror.   The apparatus having the switching element according to claim 1, wherein the switching element is a memory element for storing information.

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