Method for the manufacture of a correlated electron material device

Abstract

Disclosed is a method for the manufacture of a CEM device comprising forming a thin film of a correlated electron material having a predetermined electrical impedance when the CEM device in its relatively conductive (low impedance) state, wherein the forming of the CEM thin film comprises forming a d- or f-block metal or metal compound doped by a physical or chemical vapor deposition with a predetermined amount of a dopant comprising a back-donating ligand for the metal.

Claims

1. A method for the manufacture of a correlated electron material (CEM) device comprising forming a CEM thin film of a correlated electron material having a predetermined electrical impedance when the CEM device is in its relatively conductive (low impedance) state, wherein the forming of the CEM thin film comprises forming a d- or f-block metal or metal compound by a physical or chemical vapour deposition with a predetermined amount of a dopant comprising a back-donating ligand for the metal to impart the predetermined electrical impedance, and wherein the predetermined electrical impedance is selected to match a conductivity of the CEM device with a transductance of one or more in-series field effect transistors.

2. The method according to claim 1, comprising forming the CEM thin film by a chemical vapour deposition, such as an atomic layer deposition.

3. The method according to claim 1, comprising forming the CEM thin film to have an electrical conductivity between 10.sup.3 S/m and 10.sup.10 S/m.

4. The method according to claim 1, comprising forming the CEM thin film to have a cross-sectional area between 25 nm.sup.2 and 500 nm.sup.2.

5. The method according to claim 1, wherein the back-donating ligand for the metal is selected from the group of back-donating ligands consisting of carbonyl, nitrosyl, isocyanide, dioxygen, dihydrogen, alkene, alkyne or phosphinyl.

6. The method according to claim 1, wherein the back-donating ligand for the metal comprises one or more molecules of formula C.sub.aH.sub.bN.sub.dO.sub.f (in which a1, and b, d and f0) such as: carbonyl (CO), cyano (CN.sup.), ethylenediamine (C.sub.2H.sub.8N.sub.2), 1,10-phenanthroline (C.sub.12H.sub.8N.sub.2), bipyridine (C.sub.10H.sub.8N.sub.2), pyridine (C.sub.5H.sub.5N), acetonitrile (CH.sub.3CN) and cyanosulfanides such as thiocyanate (NCS.sup.).

7. The method according to claim 1, wherein the d-block metal or metal compound comprises nickel, iron, cobalt, ruthenium, rhodium, osmium or iridium.

8. The method according to claim 1, wherein the forming of the CEM thin film comprises forming nickel oxide with a predetermined amount of a dopant comprising a back-donating ligand for nickel.

9. A correlated electron material (CEM) device comprising a CEM thin film of a correlated electron material having a predetermined electrical impedance when the CEM device is in its conductive state wherein the CEM thin film comprises a d- or f-block metal or metal compound doped with a predetermined amount of a back-donating ligand for the metal to impart the predetermined electrical impedance, and wherein the CEM thin film has a predetermined electrical impedance selected to match a conductivity of the CEM device to a transductance of one or more in-series field effect transistors.

10. The device according to claim 9, wherein the CEM thin film has an electrical conductivity between 10.sup.3 S/m and 10.sup.10 S/m.

11. The device according to claim 9, wherein the CEM thin film has a cross-sectional area between 25 nm.sup.2 and 500 nm.sup.2.

12. The device according to claim 9, wherein the CEM thin film comprises a transition metal oxide selected from the group consisting of oxides of nickel, iron, cobalt, ruthenium, osmium, iridium and mixtures thereof.

13. The device according to claim 9, having a leakage current density (viz., a parasitic MIM diode current density) in its insulative state less than or equal to 500 A/cm.sup.2.

14. A method for tuning an electrical conductivity (or impedance) of a correlated electron material (CEM) device in its relatively conductive (low impedance) state to a transductance of one or more in-series field effect transistors in an electrical circuit, which method comprises steps of forming a first thin film of correlated electron material by a physical or chemical vapour deposition of a d- or f-block metal or metal compound which is doped by a first amount of back-donating ligand for the metal; comparing the electrical conductivity of the first thin film in its relatively conductive state to the transductance of the one or more in-series field effect transistors; and repeating these steps by forming one or more other thin films of correlated electron material each having a different amount of back-donating ligand for the metal as compared to the first thin film layer until the electrical conductivity of one of the other thin films in its relatively conductive state matches the conductivity of the device to the transductance of the one or more in-series field effect transistors.

15. The method according to claim 14, wherein the forming of the first and the one or more other thin films of correlated electron material comprises atomic layer deposition.

Description

(1) The methods and device according to the present disclosure will now be described in more detail having regard to the following embodiments and the accompanying drawings in which:

(2) FIG. 1A shows a schematic illustration of a current density versus voltage profile of a CEM switching device;

(3) FIG. 1B shows a schematic illustration of the CEM switching device of FIG. 1A and a schematic diagram of an equivalent circuit for the switching device;

(4) FIG. 2 is a schematic illustration of apparatus for implementing methods for forming the storage element;

(5) FIG. 3 is a flow diagram showing a scheme for forming a CEM switching device of FIG. 1 having a predetermined electrical impedance in its conductive state;

(6) FIG. 4 shows pulse profiles for atomic layer deposition which may be used for forming CEM switching devices having different predetermined electrical impedance in their conductive states; and

(7) FIG. 5 is a schematic illustration showing a CEM device arranged in series with one or more field effect transistors (FETs).

(8) Referring now to the accompanying drawings FIG. 2 shows an apparatus 201 for forming a thin film by atomic layer deposition (or chemical vapour deposition). The apparatus comprises a process chamber 202 connected to up line sources of a metal-containing reactant precursor 203 such as tetracarbonyl nickel Ni(CO).sub.4, a purge gas N.sub.2 and several reactant precursors 204 comprising oxidants of differing reactivity for the metal-containing reactant precursor, O.sub.2, H.sub.2O and NO. The reactivity of these reactant precursors has the order O.sub.2>H.sub.2O>NO.

(9) The process chamber 202 includes a platform (not shown) providing for the placement of a semiconductor substrate in the middle of the process chamber 202 and equipment (not shown) regulating the pressure, temperature and gas flow within the chamber in combination with a vacuum pump 204 connected to downline of the process chamber 202. The vacuum pump 204 evacuates to an abatement chamber 205 where the reactant precursors and by-products of reaction are made safe before they enter the environment.

(10) The apparatus includes a plurality of independently operable valves which help regulate the gas flow up line and downline of the process chamber. The up-line valves allow the reactant precursors and purge gas to enter the process chamber 202 sequentially and enable a selection of one or other oxidant or a particular combination of oxidants for reaction with tetracarbonyl nickel Ni(CO).sub.4 and/or the surface of the substrate.

(11) The equipment regulating the gas flow in the pressure chamber includes a mass flow controller 206 providing very precise and highly repeatable control of the amount of oxidant introduced into the process chamber in a predetermined time period.

(12) The apparatus is first prepared for use by loading the platform with the semiconductor wafer and evacuating the chamber 202 by operating the vacuum pump 204 and opening the up-line valves for the purge gas N.sub.2. During the purging, the process chamber 202 is heated to the temperature which has been selected for the thin film forming process.

(13) Referring now to FIG. 3, the use of a CEM device having desired electrical impedance in its conductive state relies upon selection of a CEM layer for the CEM device which has a predetermined electrical conductivity when the device is in its conductive state.

(14) The selection of the CEM layer may be made from a library of CEM layers of known electrical conductivity in a standard CEM switching device (similar to that described above). The library may contain sub-libraries comprising a plurality of CEM transition metal oxide layers in which each CEM layer comprises the same transition metal oxide but is doped to an extent which is different as compared to any other CEM layer. Of course, the library may also contain sub-libraries which refer to different transition metal oxides and the same or different back-donating metal ligands.

(15) The library may, for example, refer to a sub-library of CEM layers comprising nickel oxide wherein each CEM layer is doped by a carbonyl ligand to an extent which different as compared to any other CEM layer.

(16) The library may relate the electrical conductivity of a CEM layer to apparatus, reactants and parameters for obtaining the CEM layer by an atomic layer deposition. It may, for example, specify apparatus according to FIG. 2 as well as reactants and parameters for use with the apparatus.

(17) The library may specify reactants and operating parameters for apparatus that provide essentially for control of the extent of doping of the CEM layer by control of the partial pressure (or mass flow) of the oxidant during a predetermined time period.

(18) The library may, for example, indicate apparatus according to FIG. 2, tetracarbonyl nickel Ni(CO).sub.4 as the metal-containing reactant precursor 203, O.sub.2 as the oxidant, process chamber temperature, exposure times as well as partial pressure (or mass flow) of oxidant.

(19) In that case, the forming of a CEM switching device having a predetermined electrical impedance in its conductive state may comprise forming a CEM layer of a thin film of nickel oxide which is doped to a predetermined extent on the semiconductor wafer by atomic vapour deposition employing cycles of the following operations.

(20) First, the up-line valves for the purge gas are closed and the up-line valves for the are opened. After a predetermined time period in which the semiconductor wafer is exposed to and reacts with tetracarbonyl nickel Ni(CO).sub.4, the up-line valves for tetracarbonyl nickel Ni(CO).sub.4 are closed and the up-line valves for the purge gas are reopened.

(21) After a predetermined time period, the up-line valves for the purge gas are closed and the up-line valves for O.sub.2 are opened. After a predetermined time period in which the semiconductor wafer is exposed to and reacts with O.sub.2 at the specified partial pressure and temperature, the up-line valves for O.sub.2 are closed and the up-line valves for the purge gas are reopened.

(22) The number of cycles of these operations is selected to provide a thin film layer on the semiconductor wafer of a desired thickness on the semiconductor wafer.

(23) The time period during which the semiconductor wafer or thin film layer is exposed to O.sub.2 is selected so that the oxygen gas flow during that period is insufficient for complete reaction of the reactive sites on the semiconductor wafer or thin film layer with oxygen.

(24) The gas flows during this time period can be easily adjusted by the mass flow controller so that they are different. The adjustment enables a fine tuning in the amount of dopant in the thin film layer.

(25) The final nickel oxide thin film is obtained by an annealing carried out in the process chamber 202 during a predetermined time period in which purging with nitrogen is maintained. The temperature of the process chamber 202 and/or the pressure therein may be maintained or adjusted to a selected value or values during this predetermined time period.

(26) FIG. 4 shows the gas flows in the apparatus during the formation of two CEM layers having a differing extent of doping by an atomic vapour deposition as described above.

(27) The gas flows exhibit pulse profiles showing the relative amounts of metal-containing reactant precursor, oxidants and purge gas during the predetermined periods for formation of the CEM layers.

(28) As may be seen, the relative amount of oxidant for the atomic layer deposition of the CEM layer with a higher extent of doping by carbonyl is greater than the relative amount of oxidant for the atomic layer deposition of the CEM layer with a higher extent of doping by carbonyl. The predetermined time period of exposure to the semiconductor wafer is the same for each of the reactant precursors and the two oxidants.

(29) Referring now to FIG. 5, there is shown a CEM device 150 which is arranged in series with one or more field effect transistors (FETs) in a selected electronic circuit. The predetermined electrical impedance of the CEM thin film 160 when the CEM device 150 is in its conductive state is selected to match the conductivity of the CEM device 150 to the transductance of the one or more in series field effect transistors 500 (shown in solid and dotted outline).