1. FBK buried channels
Pressure test progress

2. Last meeting

3. Since then
It was observed that the O-ring used in the pressure test set-up isn’t leak tight anymore from ̴350 bars. This explains why we previously observed leaks without seeing any break or opening on the sample.
A new procedure has therefore been put in place:
It includes a pressure test only up to 300 bars
The O-ring is regularly replaced
Samples that had a water leak at pressure test but did not have any visible break were tested again

4. New procedure: logical scheme
4.1 Helium leak
test
2.2 SEM observation
3.1 Oven
He leak
No water leak
No visible failure
No water leak
No visible failure
1.1 Helium leak
test
No He leak
3.2 Replace O-ring
New pressure test
4.2 Helium bubble test to localize the leak
2.1 Pressure test up to 300 bar
Water leak
No visible failure
Water leak
No visible failure
Visible failure
Water leak
Visible failure
Water leak
Visible failure
3.3 SEM observation

5. Results on 17 samples tested with the new procedure
Three samples had a helium leak detected before the pressure test and a longitudinal aperture visible to the naked eye
Four samples had a water leak at pressure test and have a visible break of the membrane
The rest could withstand 300 bar and stay leak tight at helium test.
None leaked without having any visible opening
Case of longitudinal aperture seen before pressure test

6. Pressure Samples Longitudinal
Reminder
SINGLE: P_S_L_CX_W50 P1 W W
RAMIFIED: P_R_L_CX_W50 P1
W/#
of channels
trench
Buried channel
inlet
P1 = 25
W = 50; 100; 200; 350
W/# of channels

7. Pressure Samples Transversal
Reminder
SINGLE: P_S_T_CX_W50 P1 W
RAMIFIED: P_R_T_CX_W50 P1
W/# of channels
trench
Buried channel
inlet
P1 = 25
W = 50; 100; 200; 350

8. B3 D1 D9 F4 Sample no. Trench type (L/T12/T24) Cavity type (Single/
Ramified)
Width [μm]
(25/50/75/
100/150)
Number of
branches
(5/9/11)
Pressure at rupture
[bar]
Picture B3
Transversal
(24μm)
Single 50 5
335 D1
Longitudinal 9
334 D9
214 F4
(12μm) 25
300

9. Properties of broken membrane samples
All are Single samples
They have the largest width out of the Single samples. Out of the membrane width tested (W=25, 50, 75, 100, 150 μm), larger ones are Ramified.
All broke differently
All trench types are represented: Longitudinal (2x), Transversal 12μm (1x), Transversal 24μm (1x)
No sample with 11 branches broke: 5 branches (2x), 9 branches (2x),

10. Next
Continue the pressure test on the other wafers to have more representative results
SEM observation of broken membranes (tomorrow)
Dice samples and make pictures of channel profile
Build set-up to test the flow samples
Design of flow samples