Devices Fabrication

To realize devices which take advantages from the Josepson Junctions phenomenology, we need fabrication processes which allow to control the sample growth on tens nanometers scale. To reach such achievement we use the Shadov Mask Evaporation [1].

The Shadow Mask Evaporation (SME) is a common nano-fabrication technique by which high quality devices are obtained. The main steps of the process are:

  1. The device’s scheme is patterned on a silicon substrate coated with a bi-layer resist by the Electron Beam Lithography.
  2. Metal layer are deposited on the sample by multi-angle shadow evaporation. Insulator layer are growth by oxidation process, if needed.
  3. The bi-layer resist is removed.

The figure below shows an example of a multi-angle SME fabriction process. The upper part of the figure represents schematically the evaporation steps and the lift-off process. The lower part of the figure shows a series of Scanning Electron Micriscope (SEM) images about a proper SNS SQUID where aluminum and copper (yellow and red layer in the figure, respectively) are used as superconductor and normal metal, sepectively.

SME fabrication process of a SNS SQUID. First column: a layer of copper (red) is deposited by zero degree evaporaition on the device’s rut made by EBL technique. The proper rut of the SQUID is showed in the SEM images where the deposited copper layer is red coulored. Second column: an aluminium layer (yellow) is deposited by -30° evaporation on the same rut. By the SEM image the characteristic replicas of the device’s pattern is visible. Third column: the resists bi-layer (light grey and light blue on the figures) and the on-top metal layers are removed (lift-off process). The final device we are interested is the one marked by coulors in the SEM image: an aluminium loop interupted by two copper links.

[1] G. J. Dolan. Offset masks for lift-off photoprocessing. Appl. Phys. Lett. 31, 337 (1977)