EP1668669A2

EP1668669A2 - Material and cell structure for memory applications

Info

Publication number: EP1668669A2
Application number: EP04765710A
Authority: EP
Inventors: Recai Sezi; Andreas Walter; Reimund Engl; Anna Maltenberger; Jörg Schumann
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2003-09-30
Filing date: 2004-09-30
Publication date: 2006-06-14
Also published as: WO2005034172A2; CN1860624A; KR20060096001A; WO2005034172A3; KR100821691B1; JP2007507869A; DE10345403A1; US20060237716A1

Abstract

The invention relates to compositions for memory applications, a memory cell comprising said composition along with two electrodes, a method for producing microelectronic components, and the use of the inventive composition during the production of said microelectronic components.

Description

description

Material and cell structure for storage applications

The present invention relates to compositions for memory applications, relates to a memory cell which comprises the abovementioned composition and two electrodes, and furthermore relates to a method for producing microelectronic components and the use of the composition according to the invention in the production of these microelectronic components.

The electronic and optoelectronic applications of organic semiconductors include light-emitting diodes, field-effect transistors, devices for switching memories, memory elements, logic elements and finally complex lasers. Because industry is moving from mass-to-molecule electronics, there is an increasing trend to take a closer look at the voltage-induced switching phenomena in conjugated organic compounds that were first observed over 30 years ago.

Non-volatile and at the same time fast storage is the basic requirement for many portable devices such as Laptops, PDAs, cell phones, digital cameras, HDTVs, etc .; such devices should not require booting when turned on and a sudden power failure should not result in loss of data. For a non-volatile memory, in addition to materials with ferroelectric properties or storage elements consisting of magnetic tunnel

Junctions (MTJs) are particularly suitable for materials that can reversibly change their resistance between two stable states (resistive effect). The two different contradictions Level values can be detected via the current flow. Another advantage of the resistive memory, for example compared to the memory with a ferroelectric effect, is that the memory state is not erased when it is read out and must be written back again. Compared to memory elements consisting of MTJs, which consist of several complex layer sequences, memory elements made of resistive materials are constructed very simply.

In switching devices that can be used as memory elements, two different conductive states are observed at the same applied voltage. The two different conductive states are stable up to a certain amount of voltage and can be converted into one another if these threshold voltages are exceeded. The reversible switching back and forth between these two differently conductive states usually takes place by reversing the polarity of the voltage, the magnitude of the voltage having to be somewhat larger than the respective threshold voltages. For the detection of the two different conductive states, ie for the determination of the resistance, the applied voltage has to be below the threshold voltage so that a transfer into the other state is prevented. Several possible mechanisms have been discussed to explain the existence of the two states. The conductive states observed in thin anthracene films and in structures based on Cr-doped inorganic oxide films were attributed to the presence of traps that are filled under strong fields, which leads to high charge carrier mobility over a filamentary state. In a complicated three-layer structure, an additional metal layer was placed between two active organic layers in order to store charges and to provide switching with high conductivity (Current ratio between the two states, ON: OFF ratio = 10 ⁶ ). In these high performance devices, in which a switching mechanism is a bulky feature, their downsizing is limited to the molecular size.

In single-layer molecular switching devices, the ON-OFF ratio is generally low (50-80) and the memory lasts only minutes (approximately 15 minutes in nitroamine-based systems). The origin of the highly conductive state was traced back to the conjugation modification via an electro-reduction of the molecules. The way to increase the ON-OFF ratio is to either increase the current in the ON state or to decrease the current in the OFF state. In order to generate a molecule with a very low conducting OFF state, Bengal rose was chosen in the prior art, which has electron acceptor groups distributed over the entire surface of the molecule. In the absence of donor groups, the density of the electron distribution in the benzene rings is reduced and the conjugation in the molecule is strongly influenced.

In the publication "Large conductance switching and memory effects in organic molecules for data-storage applications" A. Bandyopadhyay et al., Applied Physics Letters, Vol. 82, No. 8, Feb. 24. 2003, switching with conductivity in Rose Bengal with a large ON-OFF ratio by restoring the conjugation of the molecules is reported. Memory effects in devices that can make these structures work in data storage applications have also been described. With the devices disclosed there, it was possible to write or erase a state and read it for many cycles. The active semiconductor kept its conductive state in switching devices upright until a reverse voltage extinguished it. A highly conductive state resulted from the restoration of the conjugation in the molecule via an electroreduction. Such a high ON-OFF ratio in a single-layer sandwich structure, compared to contemporary switching devices, is due to a low leakage current in the off state. The concept of conjugation restoration was verified in supramolecular structures by adding donor groups to the molecule, which resulted in an increased current in the off state and therefore a lower ON-OFF ratio. The above-mentioned publication shows several generalized examples of the selection of organic molecules to achieve a higher ON-OFF ratio in molecular switching devices.

In contrast, the present invention has for its object to provide a material that can be switched between two stable states of different resistivity and can therefore serve as a non-volatile memory. It is a further object of the present invention to provide a material which is used for the aforementioned purposes and by common methods in microelectronics, such as e.g. Spin coating, processable and switchable by using electrodes that are used in microelectronics. It is another object of the present invention to provide an organic material as a non-volatile memory, the material switching at low voltages.

These tasks are solved by the subject matter of the independent claims. Preferred embodiments result from the subclaims.

As mentioned above, it is known in principle that organic materials can serve as non-volatile memories. In the aforementioned publication by A. Bandyopadhyay et al. (Applied Physics Letters, Volume 82, No. 8, Feb. 24, 2003), however, describes a material that requires very laborious processing (oven treatment for several hours in a vacuum) and is also based on an indium tin oxide Electrode instructed and only switches at voltages> 3 V (see, for example, FIG. 5 by A. Bandyopadhyay et al.).

In contrast, the material according to the invention provides the particular advantage that it can be switched at voltages of 1 V.

The present invention accomplishes this by providing a new material for storage applications that includes a monomer M1 and additionally a monomer M2 and / or M3.

The present invention is particularly directed to the following aspects and embodiments:

According to a first aspect, the present invention relates to a composition for storage applications, which comprises the following constituents: a) a monomer Ml represented by the following formula 1 formula 1

where R 1, R ₂ , R ₃ and R ₄ independently of one another are H, F, Cl, Br, I, OH, SH, substituted or unsubstituted alkyl, alkenyl, alkynyl, O-alkyl, O-alkenyl, O-alkynyl, S- Alkyl, S-alkenyl, S-alkynyl, aryl, heteroaryl, O-aryl, S-aryl, 0-heteroaryl, or S-heteroaryl, - (CF ₂ ) _n - F ₃ , - CF ((CF ₂ ) _n CF. ₃ ) ₂ , - - (CF ₂ ) _n ^ ^* F ₃ , ^ F (CF ₃ ) ₂ or - ^ (CF ₃ ) ₃ ; and

n = 0 to 10; a monomer M2 and / or M3 represented by the following formulas 2 and 3:

Formula 2

Formula 3 where R ₉ , Rio, Rn, Rι ₂ independently of one another F, Cl, Br, I, CN, N0 ₂ , substituted or unsubstituted alkyl, alkenyl, alkynyl, O-alkyl, O-alkenyl, O-alkynyl, S- Are alkyl, S-alkenyl, S-alkynyl, aryl, heteroaryl, O-aryl, S-aryl, 0-heteroaryl, S-heteroaryl, aralkyl, arylcarbonyl; where Q is or

According to the invention, the combinations of the monomers Ml and M2, Ml and M3, or Ml, M2 and M3 are possible.

According to a preferred embodiment, in formula 1, R 1, R ₂ , R ₃ and R _{4 are} independently substituted or unsubstituted alkyl, O-alkyl, S-alkyl, aryl, heteroaryl, 0-aryl, S-aryl, O-heteroaryl, or S-heteroaryl.

In formula 2 and / or 3 R ₉ , Rio, Rn, R12 are preferably independently of one another Cl, CN or N0 ₂ . R ₉ , Rio, Rn, R12 in formula 2 and / or 3 are particularly preferred independently of one another

Particularly preferred monomers for Ml are tetrathiofulvalene (R1-R4 = H) and for M2 chloranil (R ₉ and Rio = Cl).

The term "alkyl" as used herein includes unbranched and branched chain alkyl groups, as well as cycloalkyl groups with 1-10, particularly preferably 1-6 carbon atoms. The terms "alkenyl, alkynyl" as used herein also relate to unbranched and branched-chain alkenyl or alkmyl groups which have 1-10, particularly preferably 1-6, carbon atoms.

The term “aryl ^{* Λ} as used herein relates to and encompasses aromatic hydrocarbon radicals preferably having 6-18, particularly preferably 6-10, carbon atoms.

According to a particularly preferred embodiment, the composition according to the invention further comprises a polymer material. With this, the monomers M1, M2 and / or M3 are formulated in a common, suitable solvent and this formulation is then problem-free, e.g. by means of spin coating, processed further.

Preferred polymer materials here are polyethers, polyether sulfones, polyether sulfides, polyether ketones, polychmolines, polychmoxalms, polybenzoxazoles, polybenzimidazoles, polyethacrylates or polyimides, including their precursors, and mixtures and copolymers thereof.

As mentioned at the beginning, the mixture is preferably dissolved in a solvent. This solvent is preferably composed of N-methylpyrrolidone, gam a-butyrolactone, methoxypropyl acetate, ethoxyethyl acetate, ethers of ethylene glycol, in particular selected diethylene glycol diethyl ether, ethoxyethyl propionate, and ethyl acetate.

As an alternative to the provision and subsequent mixing of the monomers M1, M2 and / or M3, these monomers can be chemically bound to the polymer and then dissolved in a solvent.

According to a second aspect, the present invention is directed to a memory cell comprising a composition as previously defined and two electrodes, the composition being arranged between the two electrodes.

All materials commonly used in microelectronics are suitable as electrodes, but in particular electrodes made of AlSi, AlSiCu, copper, aluminum, titanium, tantalum, titanium nitride and tantalum nitride.

The electrodes are preferably structured here, the structuring preferably being carried out by means of shadow masks or photolithographic techniques.

The layer thicknesses for the composition and the electrodes are preferably each 20 nm to 2000 nm, particularly preferably 50 nm to 200 nm.

By using adhesion promoters, the adhesion of the polymers to surfaces relevant in microelectronics such as e.g. As silicon, silicon oxide, silicon nitride, tantalum nitride, tantalum, copper, aluminum, titanium or titanium nitride can be improved. The following compounds can preferably be used as adhesion promoters:

According to a further embodiment, the memory cell is present in combination with a diode, PIN diode, Z diode or a transistor.

According to a third aspect, the invention is directed to a method for producing microelectronic components, which comprises the following steps: a) applying a first electrode to a silicon wafer, b) applying a composition as defined herein to the electrode formed in a) , c) applying a second electrode to the layer formed in b).

According to a preferred embodiment, the application in steps a) and c) takes place by means of vapor deposition or sputtering. In step b), the composition is preferably spin-coated and then dried.

According to a further preferred embodiment, the monomers contained in the composition are applied simultaneously or in succession by means of vacuum evaporation. The composition according to the invention is preferably used in the production of microelectronic components or as a storage medium.

The present invention will be explained in more detail below with the aid of the attached drawings and examples, the invention being not intended to be restricted thereby.

1 shows the exemplary cell structure of a memory cell according to the invention, comprising a silicon substrate with an SiO ₂ surface, a layer of copper (sputtered) and, as the upper layer, the materials according to the invention and titanium pads.

2 shows the circuit diagram used to measure the I (U) characteristic of the memory cell according to the invention. The SourceMeter Series 2400 from Keithley was used for the measurement.

3 shows the typical I (U) characteristic of the cells according to the invention.

Examples:

Example 1: Production of the lower electrode

On a silicon wafer with an insulating SiO or SiN surface is a vapor deposition process in a high vacuum or the metal of the lower electrode (bottom electrode) is applied by a sputtering process. All metals relevant in microelectronics such as copper, aluminum, gold, titanium, tantalum, tungsten, titanium nitride or tantalum nitride can be used as metals. The structuring of the metals can take place either by applying the metals via shadow masks or by lithographic structuring with subsequent etching of the metals applied over the entire surface by known methods.

Example 2: Preparation of polymer solutions

25g polyether, polyether sulfone, polyether ketone, polyimide, polybenzoxazole, polybenzimidazole or polymethacrylate are mixed with 5g tetrathiafulvalene and 5.98g chloroanil in 75 g dist. N-

Methylpyrrolidone (VLSI-Selectipur ^® ) or dist. γ-Butyrolactone (VLSI-Selectipur ^® ) dissolved. The dissolving process is expediently carried out on a shaker at room temperature. The solution is then pressure filtered through a 0.2 μm filter into a cleaned, particle-free sample glass. The viscosity of the polymer solution can be changed by varying the dissolved mass of polymer.

Example 3: Preparation of polymer solutions

25g polyether, polyether sulfone, polyether ketone, polyimide, polybenzoxazole, polybenzimidazole or polymethacrylate are mixed with 4g tetrathiafulvalene and 4.78g chloroanil in 75 g dist. N-methylpyrrolidone (VLSI-Selectipur ^® ) or dist. γ-Butyrolactone (VLSI-Selectipur ^® ) dissolved. The dissolving process is expediently carried out on a shaker at room temperature. The solution is then pressure filtered through a 0.2 μm filter into a cleaned, particle-free sample glass. The viscosity of the Polymer solution can be changed by varying the dissolved mass of polymer.

Example 4: Preparation of polymer solutions

25g polyether, polyether sulfone, polyether ketone, polyimide, polybenzoxazole, polybenzimidazole or polymethacrylate are mixed with 5g tetramethyl tetrathiafulvalene and 4.35 dichlorodicyanophenzoquinone in 75 g dist. N-methylpyrrolidone (VLSI-Selectipur ^® ) or dist. γ-Butyrolactone (VLSI-Selectipur ^® ) dissolved. The dissolving process is expediently carried out on a shaker at room temperature. The solution is then pressure filtered through a 0.2 μm filter into a cleaned, particle-free sample glass. The viscosity of the polymer solution can be changed by varying the dissolved mass of polymer.

Example 5: Improvement of the adhesion by means of adhesion promoter solutions

By using adhesion promoters, the adhesion of the polymers to surfaces relevant in microelectronics such as e.g. As silicon, silicon oxide, silicon nitride, tantalum nitride, tantalum, copper, aluminum, titanium or titanium nitride can be improved.

As an adhesion promoter z. B. the following connections are used:

0.5 g coupling agent (eg N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane) is dissolved in a cleaned, particle-free sample glass at room temperature in 95g methanol, ethanol or isopropanol (VLSI-Selectipur ^® ) and 5g demineralized water. After 24 hours at room temperature, the adhesion promoter solution is ready for use. This solution can be used for a maximum of 3 weeks. The adhesion promoter should result in a monomolecular layer on the surface. The coupling agent can expediently be applied by centrifugal technology. For this purpose, the adhesion promoter solution is applied over a 0.2 μm pre-filter and spun at 5000 rpm for 30s. This is followed by a drying step for 60 s at 100 ° C. Example 6: Application of a polymer by spin process

The filtered solution of the polymer according to Examples 2 to 4 is applied to the wafer using a syringe and evenly distributed with a centrifuge on the silicon wafer processed according to Example 1 or possibly processed silicon wafer pretreated according to Example 5. The layer thickness should be in the range of 50 - 500nm. The polymer is then placed on a hot plate for 1 min. at 120 ° C and for 4 min. heated to 200 ° C.

Example 7: Evaporation of the active components

In addition to the process of spinning the dissolved active components (donor and acceptor) in a polymer, the Components Ml and M2 or M3 can also be applied by the generally known method of co-evaporation. On the silicon wafer processed according to Example 1, the two components M1 and M2 are cover-vaporized, if possible in a molar ratio of 1: 1, to a layer thickness of 10-300 nm. The wafer should be cooled to 10 - 30 ° C.

Example 8: Production of the top electrode using a shadow mask

The metal of the top electrode is applied to the silicon wafer processed according to Example 6 or 7 via a shadow mask by a vapor deposition process in a high vacuum or by a sputtering process. All metals relevant in microelectronics such as e.g. Copper, aluminum, gold, titanium, tantalum, tungsten, titanium nitride or tantalum nitride can be used.

Example 9: Production of the top electrode by a lithographic process

The metal of the top electrode is applied to the entire surface of the silicon wafer processed according to Example 6 or 7 by a vapor deposition process in a high vacuum or by a sputtering process. All metals relevant in microelectronics such as copper, aluminum, gold, titanium, tantalum, tungsten, titanium nitride or tantalum nitride can be used as metals. To structure the top electrode, a photoresist is applied to the metal, exposed and structured using a spin-on process. The metal not covered with the photoresist is then removed using an etching process using known methods. The remaining photoresist is removed with a suitable stripper. Example 10: Production of the top electrode by a lift-off process

A photoresist is applied, exposed and structured on the silicon wafer processed according to Example 6 or 7 using known methods. The metal of the top electrode is then applied over the entire surface by a vapor deposition process in a high vacuum or by a sputtering process. All metals relevant in microelectronics such as e.g. Copper, aluminum, gold, titanium, tantalum, tungsten, titanium nitride or tantalum nitride can be used. The photoresist and the metal adhering to it are removed by a lift-off process.

Example 11: Measurement I (U) characteristic

The I (U) characteristic is measured in accordance with the circuit diagram shown in FIG.

The SourceMeter Series 2400 from Keithley was used for the measurement. The cells show the typical I (U) characteristic shown in FIG. 3.

The cells switch from a high-resistance state at approx. +0.6 V to Cu to a stable, low-resistance state and at - 0.3 V to Cu back to a stable, high-resistance state. These two resistively different states are stable even in the de-energized case.

Claims

claims

1. A composition for storage applications, which comprises the following components: a) a monomer Ml represented by the following formula 1

formula 1

where R 1, R ₂ , R ₃ and R ₄ independently of one another are H, F, Cl, Br, I, OH, SH, substituted or unsubstituted alkyl, alkenyl, alkynyl, O-alkyl, O-alkenyl, O-alkynyl, S- Alkyl, S-alkenyl, S-alkynyl, aryl, heteroaryl, O-aryl, S-aryl, O-heteroaryl, or S-heteroaryl, - (CF ₂ ) _n —CF ₃ , —CF ((CF ₂ ) _n CF. ₃₎ _2, -Q- (CF ₂₎ _n -CF _3, -CF (CF ₃₎ ₂ or -C (CF ₃₎ _3; and

n is 0 to 10; a monomer M2 and / or M3 represented by the following formulas 2 and 3: Formula 2

Formula 3

where Rg, Rio, Rn, R12 independently of one another F, Cl, Br, I, CN, N0 ₂ , substituted or unsubstituted alkyl, alkenyl, alkynyl, O-alkyl, O-alkenyl, O-alkynyl, S-alkyl, S- Alkenyl, S-alkynyl, aryl, heteroaryl, O-aryl, S-aryl, O-heteroaryl, S-heteroaryl, aralkyl, arylcarbonyl;

where Q is or

2. Composition according to claim 1, wherein in formula 1 Ri, R, R ₃ and R ₄ independently substituted or unsubstituted alkyl, O-alkyl, S-alkyl, aryl, heteroaryl, O-aryl, S-aryl, O-heteroaryl , S-heteroaryl.

3. Composition according to one or more of the preceding claims, wherein in formula 2 and / or 3 R ₉ , R _i0 , Rn, R _{12 are} independently Cl, CN or N0 ₂ .

4. Composition according to one or more of claims 1 or 2, wherein Rg, Rio, Rn, R12 in formula 2 and / or 3 independently of one another

are.

5. Composition according to one or more of the preceding claims, wherein Ml is tetrathiofulvalene and M2 is chloranil.

6. The composition according to one or more of the preceding claims, further comprising a polymer material,

7. The composition according to claim 6, wherein the polymer material is selected from polyethers, polyether sulfones, polyether sulfides, polyether ketones, polyquinolines, polyquinoxalines, polybenzoxazoles, polybenzimidazoles, polymethacrylates or polyimides including their precursors, and mixtures and copolymers thereof.

8. The composition of claim 6 or 7, further comprising a solvent.

9. The composition according to claim 8, wherein the solvent is selected from N-methylpyrrolidone, gamma-butyrolactone, methoxypropylacetate, ethoxyethyl acetate, ethers of ethylene glycol, in particular diethylene glycol diethyl ether, ethoxyethyl propionate, and ethyl acetate.

10. The composition according to any one of claims 6-9, wherein the monomers Ml, M2 and / or M3 are chemically bound to the polymer.

11. A memory cell comprising a composition according to one of the preceding claims and two electrodes, the composition being arranged between the two electrodes.

12. The memory cell of claim 11, wherein the electrodes are selected from AlSi, AlSiCu, copper, aluminum, titanium, tantalum, titanium nitride and tantalum nitride and combinations thereof.

13. The memory cell according to claim 11 or 12, wherein the electrodes are structured.

14. The memory cell according to claim 13, wherein the structuring takes place by means of shadow masks or photolithographic techniques.

15. Memory cell according to one or more of claims 11-14, wherein the layer thicknesses for the composition and the electrodes are each 20 nm to 2000 nm.

16. The memory cell according to claim 15, wherein the layer thicknesses are in each case 50 nm to 200 nm.

17. Memory cell according to one or more of claims 11- 16, wherein adhesion promoters are used for better adhesion of the polymers to the relevant surfaces.

18. The memory cell of claim 17, wherein the adhesion promoter comprises one of the following connections:

19. Memory cell according to one or more of claims 11-18, which is present in combination with a diode, PIN diode, Z diode or a transistor.

20. A method for producing microelectronic components, comprising the following steps: a) applying a first electrode to a silicon wafer, b) applying a composition according to any one of claims 1-10 to the electrode formed in a), c) applying a second electrode to the layer formed in b).

21. The method according to claim 20, wherein the application in step a) and c) is carried out by means of vapor deposition or sputtering.

22. The method according to claim 20 or 21, wherein the composition in step b) is spin-coated by spin coating and then dried.

23. The method according to claim 20 or 21, wherein the monomers contained in the composition are applied simultaneously or directly in succession by means of vacuum evaporation.

24. Use of a composition according to claims 1-10 in the manufacture of microelectronic components.

25. Use of the composition according to claims 1-10 as a storage and switch medium.