QUANTUM BITS AND METHOD OF FORMING THE SAME

• US 20130119351A1
• Filed: 11/11/2011
• Published: 05/16/2013
• Est. Priority Date: 11/11/2011
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Inventors: Ewing, Daniel J., Talvacchio, John J., Shea, Patrick B., Folk, Erica C.
• Granted Patent: US 9,355,362 B2
• Time in Patent Office: Days
• US Class Current: 257/31
• CPC Class Codes: G06N 10/00 Quantum computing, i.e. information processing based on quantum-mechanical phenomena
• CPC Class Codes: H10N 60/0912 of Josephson-effect devices
• CPC Class Codes: H10N 60/12 Josephson-effect devices

Abstract

Methods are provided of forming a Josephson junction (JJ) quantum bit (qubit). In one embodiment, the method comprises forming a JJ trilayer on a substrate. The JJ trilayer is comprised of a dielectric layer sandwiched between a bottom superconductor material layer and a top superconductor material layer. The method further comprises performing a thermal hardening process on the JJ trilayer to control diffusion of the dielectric layer into the bottom superconductor material layer and the top superconductor material layer, and etching openings in the JJ trilayer to form one or more JJ qubits.

Claims

1. A method of forming Josephson junction (JJ) quantum bits (qubit)s, the method comprising:

forming a JJ trilayer on a substrate, the JJ trilayer being comprised of a dielectric layer sandwiched between a bottom superconductor material layer and a top superconductor material layer;

performing a thermal hardening process on the JJ trilayer to control diffusion of the dielectric layer into the bottom superconductor layer and the top superconductor material layer; and

etching openings in the JJ trilayer to form one or more JJ qubits.

2. The method of claim 1, wherein the performing a thermal hardening process comprises annealing the JJ trilayer at a temperature between about 150°

C. to about 400°

C. for a time period between about 15 minute to about 120 minutes.

3. The method of claim 2, wherein the annealing is performed in an inert environment.

4. The method of claim 1, wherein the thermal hardening process tunes the critical current density from a first critical current density defined by the respective dimensions of the associated one or more qubits to a second current density defined by the thermal hardening process, wherein the controlled diffusion mitigates further deleterious effects caused by subsequent semiconductor processes.

5. The method of claim 1, wherein the dielectric layer is aluminum oxide (Al₂O₃), and each of the bottom and top superconductor material layers are aluminum (Al) or aluminum-copper (Al—

Cu).

6. The method of claim 1, further comprising:

depositing a protective barrier layer over the JJ trilayer;

curing the protective barrier layer;

depositing a photoresist material layer over the protective barrier layer;

irradiating and developing the photoresist material layer to form an opening pattern in the photoresist material layer;

etching the protective barrier layer to form openings in the protective barrier layer based on the opening pattern;

etching the JJ trilayer based on the openings in the protective barrier layer to form openings in the JJ trilayer layer that define a first set of superconductor material raised portions; and

stripping the photoresist material layer and the protective barrier layer.

7. The method of claim 6, wherein the protective barrier layer is cured at a temperature of about 150°

C. to about 180°

C. for about 60 to about 120 seconds.

8. The method of claim 6, wherein the top superconductive material layer is aluminum and developer utilized to develop the photoresist material layer contains sodium hydroxide, such that the protective barrier layer protects the aluminum from the sodium hydroxide during developing of the photoresist material layer.

9. The method of claim 1, wherein a protective barrier layer is employed for separate etching steps for both the top and bottom superconductor material layers.

10. A method of forming Josephson junction (JJ) quantum bits (qubits), the method comprising:

depositing a first superconductor material layer over a substrate;

forming a dielectric layer over the first superconductor material layer;

depositing a second superconductor material layer over the dielectric layer, the first superconductor material layer, the dielectric layer and the second superconductor material layer forming a JJ trilayer;

annealing the JJ trilayer in an inert environment at a temperature between about 150°

C. to about 400°

C. for a time period between about 15 minute to about 120 minutes to control diffusion of the dielectric layer into the first superconductor material layer and the second superconductor material layer; and

etching openings in the JJ trilayer to form one or more JJ qubits.

11. The method of claim 10, wherein annealing shifts the critical current density from a first critical current density defined by the respective dimensions of the associated one or more JJ qubits to a second current density defined by the annealing, wherein the controlled diffusion mitigates further deleterious effects caused by subsequent semiconductor processes.

12. The method of claim 10, wherein the dielectric layer is aluminum oxide (Al₂O₃), and each of the first and second superconductor material layers are aluminum (Al) or aluminum-copper (Al—

Cu).

13. The method of claim 10, wherein the annealing is performed after the formation of the one or more JJ qubits.

14. The method of claim 10, further comprising:

depositing a protective barrier layer over the JJ trilayer;

curing the protective barrier layer;

depositing a photoresist material layer over the protective barrier layer;

irradiating and developing the photoresist material layer to form an opening pattern in the photoresist material layer;

etching the protective barrier layer to form openings in the protective barrier layer based on the opening pattern;

etching the JJ trilayer based on the openings in the protective barrier layer to form openings in the JJ trilayer layer that define a first set of superconductor material raised portions; and

stripping the photoresist material layer and the protective barrier layer.

15. The method of claim 14, wherein the protective barrier layer is cured at a temperature of about 150°

C. to about 180°

C. for about 60 to about 120 seconds.

16. The method of claim 14, wherein a protective barrier layer is employed for separate etching steps for both the first and second superconductor material layer.

17. A plurality of Josephson junction (JJ) quantum bit (qubits) arranged on a substrate, each of the plurality of qubits comprising:

a dielectric layer;

a superconductor base layer portion underlying the dielectric layer and having a first dielectric diffused region adjacent a dielectric layer/superconductor base layer portion junction; and

a superconductor mesa layer portion overlying the dielectric layer and having a second dielectric diffused region adjacent a dielectric layer/superconductor mesa layer portion junction, the first and second dielectric diffused regions mitigating further diffusion from other semiconductor processes on the plurality of qubits.

18. The plurality of qubits of claim 17, wherein the first and second dielectric diffusion regions of a given JJ qubit define the critical current density as a second critical current density shifted from a first critical current density defined by dimension of the given JJ qubit.

19. The plurality of qubits of claim 17, wherein the dielectric layer of each qubit is aluminum oxide (Al₂O₃), and each of the superconductor base layer portion and superconductor mesa layer portion are either one of aluminum (Al) and aluminum-copper (Al—

Cu).

20. The plurality of qubits of claim 17, wherein the dielectric layer of each qubit is formed of a dielectric material that provides for hardening the superconductor-dielectric junction against junction travel and/or subsequent diffusion resulting from additional processing and each of the superconductor base layer portion and superconductor mesa layer portion are niobium (Nb).