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Vacuum Anneal

A vacuum anneal will clean your chips of organics, leave you with better contact resistances (80-95% decreases), and can partially restore a leaky gate oxide. The process works with platinum and gold electrodes. Be aware: gold electrodes seem to have less adhesion to SiO2 following a vacuum anneal. This can be seen when contacting the electrodes in the probe station. Be aware: vacuum anneals sometimes create ~μm sized 'holes' in your electrodes. This effect is likely due to photo resist residue trapped under the electrodes. So far, the holes haven't affected device performance.

  • Click Vent chamber to ATM, and open up the chamber
  • Load your samples onto the 3×3“ substrate heater 'tabletop'
    • Be sure that the thermocouple wire extending from the steel conduit is in direct contact with the heater tabletop
  • Close the chamber
  • Click Pump chamber to high vac
  • Pour some liquid nitrogen into the plastic funnel when the system switches to the diffusion pump
  • Ensure that the heater's set point is < 20 °C by holding the ★ button on the Omega temperature controller
    • To adjust the set point, hold ★ and press the ↑ or ↓ arrows
  • Plug in the heater's power cable when the pressure reaches ~5 μTorr
  • Adjust the set point in increments of 50-100 °C by holding ★ and pressing the ↑ arrow. Allow the pressure to return to ~μTorr range between increments.
    • Release ★ to see the current temperature
    • Be sure to ramp up slowly, because there is a time delay between when the coil heats up and when the thermocouple actually reads the change. This is because the thermocouple and the coil are separated by an insulator (quartz). If you ramp up quickly the coil may reach very high temperatures (and break) even though the thermocouple reports a low temp. To avoid these problems, ramp slowly to allow plenty of time for heat to move through the quartz plate and be measured by the thermocouple.
    • While ramping up the heater will 'outgas' and the chamber pressure will increase. Watch this pressure during heating, and ramp slow enough to ensure that the pressure remains < 30 μTorr. If the pressure gets too high, it's possible that your CNTs or graphene may react with these gases.
  • Set the set point to < 20 °C once you reach your desired temperature
    • Suggested ramp up value for platinum or gold electrodes: 600 °C
  • Unplug the heater's power cable
  • Allow the samples and heater to cool down
  • Click Vent chamber to ATM when the temperature is < 200 °C
    • Should take ~30 minutes
  • Open the chamber and collect your samples
  • Shutting down the system
    • Close the chamber and click Shut down system

Substrate heater

We've used a Q-series panel heater from Solar Products, Inc. These are not actually substrate heaters, they are multi-purpose heaters used for drying paint & other applications. For that reason they are much cheaper (~$385) than 'real' substrate heaters (~$1,500). To make them vacuum compatible, request that they do not put in the fibrous insulating material in the back. According to Chris Tasker, they are good in vacuum up to ~900 C.

We've used a part that was custom-made for Chris Tasker in the past (part #: OSU-3-3-120-I). The specs are 3x3x3”. High purity quartz for clean room applications. It is designed for 120 volts, and it produces 540 watts at full power. It is a stainless steel case, and non-outgassing insulating blanket is contained between two pieces of quartz – the face plate and a backup plate. This is a design that has been used in many clean room applications.

It has two 1/4 - 20 stainless steel mounting studs on the back so that it can easily be fixed in place. There are two stainless steel terminals exiting the back of the heater and you would connect your leads to those terminals. The heater can be run either face up or face down.

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