Charge dissipative dielectric for cryogenic devices
A Superconducting Quantum Interference Device (SQUID) is disclosed comprising a pair of resistively shunted Josephson junctions connected in parallel within a superconducting loop and biased by an external direct current (dc) source. The SQUID comprises a semiconductor substrate and at least one superconducting layer. The metal layer(s) are separated by or covered with a semiconductor material layer having the properties of a conductor at room temperature and the properties of an insulator at operating temperatures (generally less than 100 Kelvins). The properties of the semiconductor material layer greatly reduces the risk of electrostatic discharge that can damage the device during normal handling of the device at room temperature, while still providing the insulating properties desired to allow normal functioning of the device at its operating temperature. A method of manufacturing the SQUID device is also disclosed.
1. A thin film device comprising:
a substrate;
a first conductive material layer overlying the substrate; and
a layer of metal-insulator transition material overlying the conductive material layer;
wherein the layer of metal insulator transition material comprises a final passivation layer on top of said device;
wherein the transition material layer acts as a conductor when the device is at a first temperature to thereby protect the first conductive material layer from damage due to electrostatic discharge during handling,
wherein the transition material layer acts as an insulator when the device is at its operating temperature; and
wherein the first temperature is about 300 K and the operating temperature is about 4 K.
2. The thin film device of claim 1 , wherein the metal-insulator transition material comprises a doped silicon semiconductor material.
3. The thin film device of claim 2 , wherein the doped silicon semiconductor material comprises a doped crystalline silicon material having an MIT critical concentration N, of about 3.5×10 13 /cm 3 or less.
4. The thin film device of claim 2 , wherein the doped silicon semiconductor material has a doping level sufficient to allow the silicon semiconductor material to act as a conductor at the first temperature, and to act as an insulator when cooled to a temperature of less than about 100 K.
5. The thin film device of claim 1 , wherein the metal-insulator transition material comprises an amorphous metal semiconductor mixture.
6. The thin film device of claim 1 , wherein the conductive material layer comprises niobium.
7. The thin film device of claim 1 , further comprising a second conductive material layer overlying said first conductive material layer, said first and second conductive material layers separated by a layer of dielectric material.
8. The thin film device of claim 1 , wherein the conductive material layer has a thickness of about 10 nm to about 1000 nm.
9. The thin film device of claim 1 , wherein the layer of metal-insulator transition material has a thickness of about 25 nm to about 1000 nm.
10. The thin film device of claim 1 , further comprising a plurality of alternating layers of conductive material and dielectric material disposed between the first conductive material layer and the layer of metal insulator transition material.
11. The thin film device of claim 1 , wherein the device further comprises a plurality of contact pads, and the metal insulator transition layer contacts all of said contact pads.
12. A thin film device comprising:
a substrate;
a first conductive material layer overlying the substrate; and
a layer of metal-insulator transition material overlying the conductive material layer;
wherein the layer of metal insulator transition material comprises a final passivation layer on top of said device;
wherein the transition material layer acts as a conductor when the device is at a first temperature to thereby protect the first conductive material layers from damage due to electrostatic discharge during handling,
wherein the transition material layer acts as an insulator when the device is at its operating temperature, and
wherein the thin film device comprises a Josephson junction.
13. The thin film device of claim 12 , wherein the metal-insulator transition material comprises a doped silicon semiconductor material having a doping level sufficient to allow the silicon semiconductor material to act as an insulator when cooled to a temperature of less than about 100 K.
14. A thin film device comprising:
a substrate;
a first conductive material layer overlying the substrate; and
a layer of metal-insulator transition material overlying the conductive material layer;
wherein the layer of metal insulator transition material comprises a final passivation layer on top of said device;
wherein the transition material layer acts as a conductor when the device is at a first temperature to thereby protect the first conductive material layers from damage due to electrostatic discharge during handling;
wherein the transition material layer acts as an insulator when the device is at its operating temperature;
wherein the operating temperature is less than about 100 K
wherein the thin film device further comprises a second conductive material layer overlying said first conductive material layer, said first and second conductive material layers separated by a layer of dielectric material; and
wherein a third conductive material layer overlies said second conductive material layer, said second and third conductive material layers separated by a layer of dielectric material, and wherein the layer of metal insulator transition material overlies the third conductive material layer.
15. The thin film of claim 14 , wherein the layer of metal insulator transition material acts as a conductor when the device is at a first temperature to thereby protect at least one of the first, second and third conductive material layers from damage due to electrostatic discharge during handling, and wherein the transition material layer acts as an insulator when the device is at its operating temperature.
16. A thin film device comprising:
a substrate;
first and second conductive material layers overlying the substrate; and
a passivation layer overlying the first and second conductive material layers, said passivation layer comprising a layer of metal-insulator transition material;
wherein the passivation layer comprises a final layer on a top surface of said device; and
wherein the transition material layer acts as a conductor when the device is at room temperature to thereby protect the first conductive material layer from damage due to electrostatic discharge during handling, and the transition material layer acts as an insulator when the device is at its operating temperature.
17. The thin film device of claim 16 , wherein the passivation layer further comprises a dielectric layer overlying said layer of metal-insulator transition material.
18. The thin film device of claim 16 , wherein the device further comprises a plurality of contact pads connected with said first and second conductive material layers, and said layer of metal-insulator transition material contacts said contact pads.