FBK buried channels Pressure test progress

Last meeting

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

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

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

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

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

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

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),

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