LaCoO3 THIN-FILM DEPOSITION BY DC METAL SIMULTANEOUS SPUTTERING

Abstract

To provide a method for manufacturing a smooth and high quality crystalline LaCoO3 thin film high in a transition point from an insulator to metal and suitable for large scale production at comparatively low cost on various substrates.SOLUTION: A method for manufacturing a LaCoO3 film 60 on a substrate 38 comprises the steps of: arranging the substrate 38 in a vacuum chamber 32; arranging a cobalt target 34 in the vacuum chamber 32; arranging a lanthanum target 36 in the vacuum chamber 32; supplying oxygen 46 to the vacuum chamber 32; and sputtering the cobalt atoms 56 from the cobalt target 34 and sputtering the lanthanum atoms 58 from the lanthanum target 36 so as to interact the cobalt atoms 56 and the lanthanum atoms 58 with the oxygen to form the LaCoO3 film 60 on the substrate 38.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001]

[0001] This disclosure generally relates to a method for manufacturing a LaCoO3 film on a substrate, and more particularly, to a method for manufacturing a LaCoO3 film on a substrate that includes sputtering cobalt atoms and lanthanum atoms from two metal targets that react with oxygen in a high-vacuum sputtering chamber to produce the LaCoO3 film.

Background Art

[0002]

[0002] In receiver front-end circuits and other devices, RF power limiters are often used to protect sensitive electrical components, such as low noise amplifiers (LNAs), from high-power RF signals. Conventionally, these power limiters are solid-state devices that use semiconductor components, such as p-i-n diodes and MESFET devices, to limit the input power within a specific frequency range. However, with the advancement of RF components and system power and agility, additional challenges in the form of low power consumption, higher incident power control, and high reliability are being imposed on conventional RF power limiters. These challenges have led to an investigation of new power-limiting materials that often employ an insulator-to-metal phase transition (IMT) in response to specific temperature changes that increase with increasing power. In response to an increase in current, i.e., an increase in temperature, the IMT material transitions from an insulating state to a metallic state and shunts power exceeding a given threshold.

Summary of the Invention

Problems to be Solved by the Invention

[0003]

[0003] One IMT material that can exhibit IMT behavior for power limiting purposes is vanadium dioxide (VO2). VO2 is synthesized by various methods, including molecular beam epitaxy (MBE), pulsed laser deposition, and DC and radio frequency sputtering. VO2 exhibits a sharp drop in resistance when the material is heated to approximately 340 Kelvin. However, this temperature is generally too low for the actual device operation of many systems.

[0004]

[0004] Another IMT material that can exhibit IMT behavior is lanthanum cobalt oxide (LaCoO3). LaCoO3 has IMT at higher temperatures than other IMT materials such as VO2. More specifically, LaCoO3 shows a significant decrease in resistivity at about 500 Kelvin as a result of non-structural phase transitions such as electron spin state transitions or orbital melting mechanisms, and its electrical resistivity decreases rapidly as a function of increasing temperature. Since much of the research on the material is focused on its catalytic applications in gas and humidity sensors, typical synthesis methods of LaCoO3 found in the literature focus on the creation of porous volumes. Various processes for depositing thin films of LaCoO3 have been reported in the literature, and these typically focus on catalytic applications such as MBE, ion beam sputtering, chemical vapor deposition, and pulsed laser deposition. MBE is known to produce high-quality, smooth crystalline films. However, it is a time-consuming, difficult, and expensive process. According to the literature, LaCoO3 films can be fabricated using DC simultaneous sputtering of a metal target, but these processes require a post-deposition calcination step to properly oxygenate and crystallize the film. [Brief explanation of the drawing]

[0005] [Figure 1] This is a schematic block diagram of a power limiter using a LaCoO3 film. [Figure 2] This is a schematic block diagram of a sputtering system for manufacturing LaCoO3 films. [Modes for carrying out the invention]

[0006]

[0007] The following discussion relating to embodiments of the present disclosure directed to a method for fabricating a LaCoO3 film on a substrate is essentially illustrative and is not intended in any way to limit the present disclosure or any use or application of it.

[0007]

[0008] This disclosure proposes the fabrication of RF devices using LaCoO3 films whose resistance rapidly decreases as the temperature rises above a threshold. The challenge is to fabricate smooth, high-quality crystalline thin LaCoO3 films on various substrates that have a high insulator-to-metal transition temperature and are suitable for large-scale production at relatively low cost. Furthermore, for simplicity and to protect the underlying device layers from damage during high-temperature firing, the process should consist of only one step. This process allows for the deposition of LaCoO3 films on various substrates with different dielectric properties to optimize film properties and device performance.

[0008]

[0009] To provide the RF devices described above, this disclosure describes a single-step DC sputtering process for synthesizing LaCoO3 using relatively inexpensive raw materials that can be rapidly manufactured in large wafer-scale quantities. Rather than using a pre-sintered LaCoO3 ceramic target, the proposed process utilizes less expensive lanthanum and cobalt metal targets. This process uses a heated substrate in combination with the deposition of a metal target in an active oxygen / argon atmosphere. These metals are vaporized by a DC magnetron gun that emits the material toward the substrate. Under these conditions, the metals react and crystallize directly onto the substrate surface, forming a LaCoO3 film. Thus, no secondary processing steps are required to fully crystallize or oxygenate the film. An additional advantage of the proposed process is that, by using independently controlled metal targets, the composition of the film can be adjusted, allowing for finer control over the optimization of film properties. The ability to vary the substrate temperature in this process also allows for balancing the advantages of highly crystalline films grown at 700°C and amorphous films grown at lower temperatures. Furthermore, while it is possible to produce smooth, high-quality films, sputtering is considered a low-cost, high-speed manufacturing tool used for large-scale wafer synthesis.

[0009]

[0010] Figure 1 is a schematic block diagram of a power limiter 10 that limits the amount of power that can be delivered to a sensitive electrical device 12, such as an LNA. The input signal is supplied to a waveguide 14 that delivers the signal to the device 12. A LaCoO3 film 16 is formed on one side of the waveguide 14 and coupled to a ground element 18, and a LaCoO3 film 20 is formed on the opposite side of the waveguide 14 and coupled to a ground element 22. As the power of the input signal increases, more heat is generated in films 16 and 20. When the thermal levels of films 16 and 20 are below a certain threshold, films 16 and 20 are insulators and the signal propagates directly through the waveguide 14 to the device 12. When the thermal levels of films 16 and 20 reach the threshold, films 16 and 20 transition to metal and become conductive, and the power of the signal is diverted through films 16 and 20 to the ground elements 18 and 22, with the minimum power being delivered to the device 12. When the thermal levels of films 16 and 20 fall below a threshold, films 16 and 20 transition back to insulators.

[0010]

[0011] Figure 2 is a schematic block diagram of the sputtering system 30, including the vacuum chamber 32. The cobalt source target 34 and the lanthanum source target 36 are positioned together with the chamber 32 relative to the substrate 38, which is intended to represent any substrate of a suitable material such as silicon carbide, sapphire, fused silica, silicon, lanthanum aluminate, or a fully fabricated device such as a GaN wafer. Depending on the application, the substrate 38 may be heated by a heater 40 to a desired temperature, for example, between 400°C and 700°C, to enhance the sputtering process. Argon or other suitable inert gas from the supply source 44 and oxygen from the supply source 46 are released into the chamber 32, thereby increasing the pressure inside the chamber 32 to, for example, 5 mtorr.

[0011]

[0012] Negative bias potentials are applied to targets 34 and 36, respectively, by DC sources 52 and 54. The ionization frequency is increased by trapping electron clouds near the surfaces of targets 34 and 36 using magnets (not shown), thereby increasing the likelihood of argon gas collisions and ionization. Positive argon ions collide with targets 34 and 36, releasing cobalt atoms 56 from target 34 and lanthanum atoms 58 from target 36. Atoms 56 and 58 are attracted to the substrate 38, where they react directly with oxygen to form a crystallized LaCoO3 film 60 on the substrate 38. A rotating device 62 rotates the substrate 38 so that the film 60 has uniform concentrations of cobalt and lanthanum. The sputtering process continues until the film 60 reaches a desired thickness, e.g., 40–200 nm. The oxygen percentage in the chamber 32 is carefully adjusted to avoid significant oxidation of targets 34 and 36.

[0012]

[0013] The foregoing discussion discloses and describes only exemplary embodiments of the present disclosure. Those skilled in the art will readily recognize from such discussion, as well as the accompanying drawings and claims, that various changes, modifications, and variations can be made without departing from the spirit and scope of the present disclosure as defined in the following claims.

Claims

1. LaCoO on the substrate ３ 1. A method for producing a membrane, comprising: placing the substrate in a vacuum chamber; placing a cobalt target in the vacuum chamber; disposing a lanthanum target in the vacuum chamber; supplying oxygen into the vacuum chamber; Cobalt and lanthanum atoms interact with the oxygen to form the LaCoO ３ sputtering the cobalt atoms from the cobalt target and the lanthanum atoms from the lanthanum target to form a film; A method comprising:

2. The method of claim 1 , further comprising the step of heating the substrate.

3. The method of claim 2 , wherein heating the substrate comprises heating the substrate to a temperature between 400° C. and 700° C.

4. The method of claim 1 , further comprising rotating the substrate.

5. 2. The method of claim 1, wherein sputtering the cobalt and lanthanum atoms comprises generating an inert gas plasma in the chamber and biasing the cobalt and lanthanum targets to bombard the targets with plasma ions.

6. The method of claim 5 wherein the inert gas is argon.

7. The method of claim 1 , wherein the substrate is part of a power limiter.

8. LaCoO on the substrate ３ 1. A system for producing a membrane, comprising: means for placing the substrate in a vacuum chamber; means for positioning a cobalt target within said vacuum chamber; a means for positioning a lanthanum target within said vacuum chamber; means for supplying oxygen into said vacuum chamber; Cobalt and lanthanum atoms interact with the oxygen to form the LaCoO ３ means for sputtering the cobalt atoms from the cobalt target and the lanthanum atoms from the lanthanum target to form a film; A system comprising:

9. The system of claim 8 further comprising a means for heating the substrate.

10. 10. The system of claim 9, wherein the means for heating the substrate heats the substrate to a temperature between 400°C and 700°C.

11. The system of claim 8 further comprising means for rotating the substrate.

12. 9. The system of claim 8, wherein the means for sputtering cobalt and lanthanum atoms generates an inert gas plasma in the chamber and biases the cobalt and lanthanum targets to bombard the targets with plasma ions.

13. The system of claim 12 , wherein the inert gas is argon.

14. The system of claim 8 , wherein the substrate is part of a power limiter.

15. 1. A power limiter for limiting power applied to an electronic device, comprising: a waveguide for receiving an input signal to be transmitted to the electronic device; At least one LaCoO ３ A membrane, The at least one LaCoO ３ At least one ground element formed on the film, the at least one LaCoO ３ When the heat level of the film falls below a predetermined threshold, the at least one LaCoO ３ The film becomes an insulator, and the input signal propagates directly through the waveguide to the electronic device, and the at least one LaCoO ３ When the heat level of the film reaches the threshold, the at least one LaCoO ３ The film is conductive, and the input signal is applied to the at least one LaCoO ３ at least one ground element shunted through a membrane to the at least one ground element; A power limiter comprising:

16. The at least one LaCoO ３ The film is a first LaCoO ３ A second LaCoO film is formed on the opposite side of the waveguide. ３ a LaCoO film, and the at least one ground element is the first LaCoO ３ A first ground element formed on the film and the second LaCoO ３ 16. The power limiter of claim 15, wherein the second ground element is formed on the membrane.

17. The at least one LaCoO ３ The power limiter of claim 15, wherein the film has a thickness of 40 to 200 nm.

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