Introduction
The device structure is Al-A2O3-Pb.
Substrate -
I am using glass as substrate for fabrication of IETS devices.
Cleaning of the substrate
First Lot of Fabricated Devices
Pb 500nm
Second lot of Fabricated Devices -
Date - 03/19/13
Fabrication Steps
Step -1 : Deposited 100nm Al on pre-cleaned glass substrate using thermal physical vapor deposition at 5x10^-6mbar pressure.
Step -2: The devices was in deposition vacuum chamber for around 12 hours. The devices was than exposed to air for 6 hours for growing Al2O3 which will act as tunneling barrier. For doping tunneling junction, Acetophenone was spin coated on grown Al2O3 at 6000rpm.
Step -3: 100nm of Pb was deposited on cross electrode geometry using thermal physical vapor deposition system. The devices were kept in vacuum chamber for around 1 day.
The resistance between two terminal of one of the electrode was infinity making these devices useless. Possible reason of this could be that the thickness of the electrode were too thin (~100nm). I am not sure which electrode was showing infinite resistance but I suspect its mostly Pb electrode.
Calculation for resistance of the electrodes
Lead Pb:
L = 6mm, b = 1mm, t = 100nm and p = 208nohm.m so calculated R = 12ohm
Aluminum Al
L = 6mm, b = 1mm, t = 100nm and p = 28nohm.m so calculated R = 1.6ohm
Cause of failure - I am assuming its because of the thickness of the Pb electrode. At the junction, there could be discontinuity because of the step at the junction area (the thickness of the Al/Al2O3 at device area is 100nm+ ). Since the height difference is more ~100nm+oxide thickness and Pb deposited height is around 100nm, there could be discontinuity at the junction in Pb electrode. Another reason could be that because of small thickness of the electrode, indium in not making good contact.
I am gonna fabricated another set of devices with this time electrode thickness of ~200nm for Al and 500nm for Pb. I am also gonna check the resistance of the Al electrode to make sure which metal electrode is showing infinite resistance.
Third LOt of Fabricated Devices -
03/21/13
This time, I deposited 80nm of Aluminum using Tungsten boat (as alumina coated Tungsten boat was giving me hard time). After ~1hour, I opened the chamber and removed the devices and checked its device resistance. The resistance of the aluminum lead was 67ohms. I immediately changed the orientation of the device and kept it inside the chamber for Pb deposition. The time should be around ~10min so I just gave this much time for the oxidation of aluminum. After that I deposited 500nm of Pb. This time there was no infinite resistance of any lead so I concluded that previously the infinite resistance was shown by Pb leads and it was because of the discontinuity in the Pb electrod at the junction. The resistance of the Pb electrode was 21ohm. The resistance of the Pb electrode seems to increase with time. The device impedance could be of the order of 1ohm because when I applied 1mA current and used four probe method to measure the voltage, it was about 1.1mV.
The device structure is Al-A2O3-Pb.
Substrate -
I am using glass as substrate for fabrication of IETS devices.
Cleaning of the substrate
First Lot of Fabricated Devices
Pb 500nm
Second lot of Fabricated Devices -
Date - 03/19/13
Fabrication Steps
Step -1 : Deposited 100nm Al on pre-cleaned glass substrate using thermal physical vapor deposition at 5x10^-6mbar pressure.
Step -2: The devices was in deposition vacuum chamber for around 12 hours. The devices was than exposed to air for 6 hours for growing Al2O3 which will act as tunneling barrier. For doping tunneling junction, Acetophenone was spin coated on grown Al2O3 at 6000rpm.
Step -3: 100nm of Pb was deposited on cross electrode geometry using thermal physical vapor deposition system. The devices were kept in vacuum chamber for around 1 day.
The resistance between two terminal of one of the electrode was infinity making these devices useless. Possible reason of this could be that the thickness of the electrode were too thin (~100nm). I am not sure which electrode was showing infinite resistance but I suspect its mostly Pb electrode.
Calculation for resistance of the electrodes
Lead Pb:
L = 6mm, b = 1mm, t = 100nm and p = 208nohm.m so calculated R = 12ohm
Aluminum Al
L = 6mm, b = 1mm, t = 100nm and p = 28nohm.m so calculated R = 1.6ohm
Cause of failure - I am assuming its because of the thickness of the Pb electrode. At the junction, there could be discontinuity because of the step at the junction area (the thickness of the Al/Al2O3 at device area is 100nm+ ). Since the height difference is more ~100nm+oxide thickness and Pb deposited height is around 100nm, there could be discontinuity at the junction in Pb electrode. Another reason could be that because of small thickness of the electrode, indium in not making good contact.
I am gonna fabricated another set of devices with this time electrode thickness of ~200nm for Al and 500nm for Pb. I am also gonna check the resistance of the Al electrode to make sure which metal electrode is showing infinite resistance.
Third LOt of Fabricated Devices -
03/21/13
This time, I deposited 80nm of Aluminum using Tungsten boat (as alumina coated Tungsten boat was giving me hard time). After ~1hour, I opened the chamber and removed the devices and checked its device resistance. The resistance of the aluminum lead was 67ohms. I immediately changed the orientation of the device and kept it inside the chamber for Pb deposition. The time should be around ~10min so I just gave this much time for the oxidation of aluminum. After that I deposited 500nm of Pb. This time there was no infinite resistance of any lead so I concluded that previously the infinite resistance was shown by Pb leads and it was because of the discontinuity in the Pb electrod at the junction. The resistance of the Pb electrode was 21ohm. The resistance of the Pb electrode seems to increase with time. The device impedance could be of the order of 1ohm because when I applied 1mA current and used four probe method to measure the voltage, it was about 1.1mV.
No comments:
Post a Comment