2014-03

2014-03Edit

vendredi 28/03

BPC1_5

Q-type sample with ground plane and single resonator.

Idea: Reducing quasiparticle poisoning by simplifying the design. This includes: Removing one of the DC gates, decreasing overall size of the island, increasing gate-to-island distance as well as increasing overlap area in order to diminish possible fabrication problems.
Exposure:  30 kV, Spot 1
dev: as usual: MIBK/IPA=90s, IPA=30s, ODI=15s, MIF726=60s, ODI=60s, Ethanol=15s. Gentle N2 dry.
obtical microscope: Bottom left (i.e. single SQUID)= cracks  in the resist. Design was probably exposed twice (mistake).
top left=structure was not exposed but alignment markers were, maybe happened by mistake.
top center (4 test SQUIDS)= cracks in the resist.
top right= SQUID looks fine. Bottom right=not well aligned and is therefore shifted to the outside of the desired area.
Evap:  No Argon milling as the filament broke. Al30.prg@22deg, dynamic O2 for 5min at around 0.1+ Torr, Al60.prg@-22deg.
Lift-off: Extensive use of low power Ultrasonic bath.
Obs: SEM images -> BPC1_5.rar. Undercut was too small as the shift was only around 150nm between the two deposited layers and no overlaps were created for the JJ's. Except for the top right SQUID which has a the expected 600nm shift and the right dimension. The top right structue shows an inhomogeneous shape which might be related to the skipped Ar milling.

lundi 31/03

BPC1_6

Q-type sample with ground plane and single resonator.

Idea: Same design as in BPC1_5 but increasing the overlap between adjoined rectangles. Reducing MIF726 dev. time to reduce the cracks in the PMMA resist. Performing Ar milling and avoiding Ultrasonic bath during liftoff.
Exposure:  30 kV, Spot 1
dev: as above but with MIF726=45s
obtical microscope: All structures look nice and only a few, short cracks are visible.
Evap:  Argon milling, Al30.prg@22deg, dynamic O2 for 5min at around 0.1+ Torr, Al60.prg@-22deg, O2-flush before venting the loadlock to create an oxyde layer with pure O2.
Lift-Off:  No use of the Ultrasonic. 25min in the 60 deg Celsius PGremover was enough.
Obs: SEM images ->BPC1_6.zip.Undercuts are in the right range now and give a shift of around 620 nm between the two evaporated layers. Main problem is are the possible cracks between the island and the lead which short circuit the junction, see DC SQUIDS.pdf (T- and I-shaped ilsands for 2 different doses each). The T-shaped island looks slightly better.

mardi 01/04

Strain1

Test sample from "BPC1 2014-01-30".

Idea: Reduce overall exposure area in order to reduce strain in the mask, especially around the junction/SQUID and island. Using a test sample. Also add a structure with the previous gate design. Two designs -> CPB1_ebeam__DC_strain_reduction Zoom 1.pdf. For each of these designs the doses of certain structures are varied (4x4 Matrix, labelled by row A-D and column 1-4). A and B row have two simple recangular gates whereas row C and D have the T-shape gates.
A1-A3: horizontal part of SQUID D=1.1-1.2.
A4: gates d=0.95 and horizontal part of SQUID d=1.1.
B-row is identical to A-row.
C1-C3: same as A1-A3.
C4: similar to A4 but with increase of dose of the close gate structures to d=1.05.
D-row is identical to C-row.
Exposure:  30 kV, Spot 1
dev: as above with MIF726=60s
obtical microscope: Only a few very small cracks. Generally looks fine
Evap:  Ar milling and TwoAngleAu.prg evaporation, each 30 nm. It was difficult to align meaning that the evap had an error of up to 15 degree in the x-y plane.
Lift-Off:  20 min in PGRemover at 60 deg C, no US.
Obs: SEM images -> Strain1.zip Crack between Island and the closest junction lead. Horizontal junction leads are not visible.

mercredi 02/04

Strain2

Test sample from "BPC1 2014-01-30".

Idea: Increase distance between island and horizontal lead to reduce stress (as the crack always goes to the closest horizontal lead for "Strain1"). Going back to T-shape of the island as the junctions are at the same vertical height. Additonally the ground lead (top of the SQUID) should be wider to have a better overlap between the two deposited layers.

For each of these designs the doses of certain structures are varied (4x4 Matrix, labelled by row A-D and column 1-4). A and B row have two simple recangular gates whereas row C and D have the T-shape gates (see figures above).
A1-A4: horizontal part of island d=1.15-1.3 (left figure).
B1-B4: Horizontal part of SQUID |_ _| ("le crabe") , d=1.05-1.2 (left figure).
C1: T-gate (right figure).
C2-C4: Horizontal part of SQUID |_ _| replaced by 7 single lines (stacked), d=1.1-1.2 (right figure).
C4: similar to A4 but with increase of dose of the close gate structures to d=1.05.
D-row is identical to C-row.
Exposure:  30 kV, Spot 1
dev: as above with MIF726=60s
obtical microscope: Large cracks visible. The island and the SQUIDs are not visible. Sometimes large undercut rings around the structure which seem to be correlated to large cracks. OptMicroAfterDev.pdf

Evap:  Ar milling and TwoAngleAu.prg evaporation, each 30 nm. Aligning was good this time.
Lift-Off:  20 min in PGRemover at 60 deg C, no US.
Obs: SEM images ->  Strain2.zip .Island and SQUIDs are not visible. Lots of cracks as expected. Typical image:

Additonally the old design was exposed "DC_v1" and the large undercut is visible but otherwise the same problem as above:

mercredi 02/04 et jeudi 03/04

Strain3

Test sample from "BPCD7 (05/12/2013)".

Idea: Same as "Strain2" but on different sample. Exposure 3 time the same 4x4-Matrix but with different overal dose factors (0.9, 1.0, 1.1) and also exposuring the previous "DC_v1" design.
Exposure:  30 kV, Spot 1, done in the evening of the 02/04
dev: as above with MIF726=60s, done in the morning of the 03/04
obtical microscope: Generally looks fine (opt microscope Dose factor 1.0.pdf)

Evap:  Ar milling and TwoAngleAu.prg evaporation, each 30 nm.
Lift-Off:  20 min in PGRemover at 60 deg C, no US.
Obs: SEM images -> Strain3.zip. Conlusions:
-Use the rectangular gates
-increase left gate gap by 25nm and decrease right gate gap by 25nm
-use the 7 single lines for the arms of "le crabe" with dose 1.2+
-reduce dose of top lead (with width 800nm) to 0.9 in order to reduce mechanical stress inside the SQUID-loop

Strain4

Test sample from "BPCD7 (05/12/2013)".

Idea: Same as "Strain3" but with the above mentioned changes.
A1-A4: The top of the T-shaped island consists of 4 lines with dose=1.3-1.45
B1-B4: arms of "le crabe" consists of 7 lines with dose=1.2-1.35
C1-C4: vertical part of T-island as rectangle with dose=1.15-1.3
D1-D4: vertical part of T-island consits of 4 lines, all with with dose=1.2-1.35
Exposure:  30 kV, Spot 1,
dev: as above with MIF726=60s
obtical microscope: Generally looks fine.
Evap:  Ar milling and TwoAngleAu.prg evaporation, each 30 nm.
Lift-Off:  20 min in PGRemover at 60 deg C, no US.
Obs: SEM images -> Strain4.zip. Conlusions:
-Use single vertical lines for the islansd with dose 1.35
-reduce the vertical part of the T-island to 3 single lines
-horizontal part of the T-island should have a dose of around 1.4+
-for the arms of le crabe: remove 1 or 2 lines from the top and test dose
-do a better focus on the 3 points before exposure.

Strain5

Test sample from "BPCD7 (05/12/2013)".

Idea: Implementation of the above conlusions (see Strain4) plus:
A1-A4: removed 1 line of the vertical part of the T-island (removed from the top) and dose=1.3-1.45
B1-B4: removed 1 line of each crabe arm (so there are 5 left) and dose=1.25-1.4
C1-C4: like B1-B4 but with 6 lines
D1-D4: vertical part of T-island consits of 4 lines, dose=1.25-1.4

Additonally the "DCv1" design was added to cross-check.

Exposure:  30 kV, Spot 1, "DC_strain_red_DoseTest1"
dev: as above with MIF726=60s, stiring the sample very gentle.
obtical microscope: Generally looks fine, no cracks.
Evap:  Ar milling and TwoAngleAu.prg evaporation, each 30 nm.
Lift-Off:  20 min in PGRemover at 60 deg C, no US.
Obs: SEM images Strain5.zip. DCv1.zip.