ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 3D Trenched-Electrode Sensors for Charged Particle Tracking and Timing R. Mendicino 1,2 , M. Boscardin 3,2 , G. T. Forcolin 1,2 , A. Lai 4 , A. Loi 4,5 , S. Ronchin 3,2 , S. Vecchi 6 , G.-F. Dalla Betta 1,2 1 University of Trento, Trento, Italy 2 TIFPA INFN, Trento, Italy 3 Fondazione Bruno Kessler, Trento, Italy 4 INFN Sezione di Cagliari, Cagliari, Italy 5 University of Cagliari, Cagliari, Italy 6 INFN Sezione di Ferrara, Ferrara, Italy Argonne, 11-14 September 2018
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 2 Outline • Introduction: 3D Sensors • Timing with 3D-trench sensors • Design and technological aspects • TCAD simulation results • Process development and sensor layout • Conclusions
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 3 3D sensors S. Parker et. Al. NIMA 395 (1997) 328 Electrode distance (L) and active substrate thickness ( D ) are decoupled à L<< D by layout ADVANTAGES: - Low depletion voltage (low power diss.) HIGH RADIATION HARDNESS - Short charge collection distance: DISADVANTAGES: - Fast response • Non uniform spatial response - Less trapping probability after irr. (electrodes and low field regions) - Lateral drift à cell “shielding” effect: • Higher capacitance with respect - Lower charge sharing to planar (~3-5x for ~ 200 µ m thickness) - Low sensitivity to magnetic field • Complicated technology (cost, yield) - Active edges
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 4 Timing: Planar vs 3D 4. " 4. " 4. " 1. 3D lateral cell size can be smaller than wafer 1. shorter collection distance thickness, so 2. in 3D, field lines end on electrodes of larger 2. higher average fields for any given area, so maximum field (price: larger electrode capacitance) 3. most of the signal is induced when the charge is close to the electrode, so planar signals are spread out in time as the charge 3. 3D signals are concentrated in time arrives, whereas as the track arrives 4. Landau fluctuations along track arrive 4. Landau fluctuations (delta ray sequentially and may cause secondary ionization) arrive nearly peaks simultaneously
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 5 Speed with 3D S. Parker et al. IEEE So far tested with hex-cell 3D’s TNS 58(2) (2011) 404 (L=50 µ m) & fast current amplifier dt - 50% constant fraction dt - fit waveform analysis mean - fit 177 ps 100 time (ps) 31 ps s noise ~ 0.33 mV 10 2 3 4 5 6 7 8 9 10 20 pulse height (mV)
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 6 3D Trenched-electrode sensors S. Parker et al. IEEE TNS 58(2) (2011) 404 signal electrodes with contact next section offset so pads to readout signal electrodes do not line up 200 – 300 µm active edge Benefits from trench electrodes • High average field / peak field • Uniform Ramo’s weighting field beam in • Initial pulse time independent of the track position Possible issues Schematic diagram of multiple plane arrangement • Fabrication complexity in an active-edge 3D trench-electrode detector. Other offsets (⅓, ⅔, 0, ⅓, ⅔ ..etc.) may also be used. • Electrode capacitance
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 7 3D technology: where we stand S. Ronchin, >150 µ m FBK 5 µ m • Very impressive progress made in the past few years • High aspect ratio (depth/width) DRIE feasible: up to 30:1 and beyond for columnar electrodes, even better for trenches ( > 40:1) • Flexibility in the choice of active thickness and inter-electrode distance (small pitch feasible) • High breakdown voltage can be achieved also before irradiation, allowing for large V bias range !
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 8 Schematic design p + trench pitch n + trench (a) Strip pitch-x p + trench pitch-y width gap n + dashed (b) Pixel trenches • Pixel pitch (55 µ m) chosen to be compatible with TIMEPIX ROC • Trenches are dead volume, they should be as narrow as possible (~4 µ m) • n + trench width (gap) to be optimized with the aid of TCAD simulations
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 9 Impact of the gap (1): electric field gap=16 µ m strip (no gap) gap=14 µ m gap=12 µ m gap=10 µ m gap=8 µ m Plots show the difference with respect to the strip (no gap) situation
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 10 Impact of the gap (2): electron velocity gap=16 µ m strip (no gap) gap=14 µ m gap=12 µ m gap=10 µ m gap=8 µ m Plots show the difference with respect to the strip (no gap) situation
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 11 Impact of the gap (3): hole velocity gap=16 µ m strip (no gap) gap=14 µ m gap=12 µ m gap=10 µ m gap=8 µ m Plots show the difference with respect to the strip (no gap) situation
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 12 Impact of the gap (4): weighting field gap=16 µ m gap=14 µ m gap=12 µ m gap=10 µ m gap=8 µ m gap=6 µ m • As expected, the weighting field distribution is confined within neighbors pixel • The gaps cause a significant distortion with respect to the uniform case (strip)
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 13 Weighting field: more in detail gap=16 µ m gap=14 µ m gap=12 µ m gap=10 µ m gap=8 µ m gap=6 µ m High dependence with Low dependence with geometry geometry
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 14 Impact of the gap (5): MIP signals Using TCAD HeavyIon x model x x d 3 Hit positions (X): 3 Trench widths: 1) x =13.75 µ m, y = 12.5 µ m 1) 41 µ m à d= 14 µ m 2) x = 27.5 µ m, y= 12.5 µ m 2) 45 µ m à d= 10 µ m 3) x = 27.5 µ m, y = 0 µ m 3) 49 µ m à d= 6 µ m
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 15 Signal comparison At 100 V 100V: x=13.75 y=12.5 100V - - ´ 6 ´ 6 10 10 Current (A) Current (A) µ µ 41 m 41 m x=13.75 y=12.5 14 14 1 1 µ x 45 m µ 41 m x=27.5 y=0 12 12 µ 49 m µ 41 m x=27.5 y=12.5 d 10 µ 10 45 m x=13.75 y=12.5 µ 45 m x=27.5 y=0 8 8 µ 45 m x=27.5 y=12.5 2 6 6 µ 49 m x=13.75 y=12.5 µ 4 4 49 m x=27.5 y=0 3 µ 49 m x=27.5 y=12.5 2 2 At 100 V 0 - 0 - ´ 9 ´ 9 10 10 0 1 2 3 4 5 0 1 2 3 4 5 Time (s) Time (s) 100V: x=27.5 y=12.5 100V: x=27.5 y=0 - - ´ ´ 6 6 10 10 Current (A) Current (A) µ µ 41 m 41 m 14 14 2 3 µ µ 45 m 45 m µ µ 12 12 49 m 49 m x x d d 10 10 8 8 6 6 4 4 2 2 At 100 V At 100 V - - 0 ´ 9 0 ´ 9 10 10 0 1 2 3 4 5 0 1 2 3 4 5 Time (s) Time (s)
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 16 Radiation hardness % & = −) ⃗ " * # $ • Ramo’s Theorem with from input from TCAD: ü ⃗ " is the drift velocity of charge carriers ü (Electric field à charge trajectory and velocity) ü # $ is the “weighting Field” à charge motion coupling to a specific electrode + , = + - . / 0 , 1 ü Charge trapping included: • New Perugia model (bulk damage): F. Moscatelli et al., IEEE TNS 64 (2017) 2259 • Very high signal efficiency expected
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 17 Pixel: technological constraints Existing FBK 3D-SS process 20 junction Ohmic p-spray 4 4 Device layer Support wafer 4 Si-Si Direct Wafer Bonding Minimum distance between trenches Minimum distance between metals …
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 18 Pixel: from schematic to layout Bump pad p-poly-cap p-poly-cap Bump pad Contact hole ohmic ohmic junction Contact hole • Modified process with additional oxide layer between poly and metal • More design flexibility: no need for full metal overlap to poly • Ohmic columns are better isolated • Removal of p-poly-cap would increase distance to bump pad
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 19 Full-3D simulation of capacitance Bump pad Metal ( N-contact) Oxide N - T r e n c h e s + P o l y - S i 1 5 0 55 µ m µ m P-Trenches + poly-Si Metal (P-contact )
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 20 Considered geometries Trench Length: Trench Length: 41 µ m 41 µ m 43 µ m 43 µ m 45 µ m 45 µ m 47 µ m 47 µ m 49 µ m 49 µ m Thin metal Thin metal poly Trench Length: Trench Length: 41 µ m 45 µ m 43 µ m 45 µ m 47 µ m Bump Wide metal
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 21 Simulated capacitance (1): components Thin Metal poly, C-V - ´ 12 10 0.1 Capacitance (F) µ µ 41 m g1-g2 41 m g1-back µ µ 0.09 43 m g1-g2 43 m g1-back µ µ 45 m g1-g2 45 m g1-back Backplane (1x) 0.08 µ µ 47 m g1-g2 47 m g1-back 0.07 µ µ 49 m g1-g2 49 m g1-back 0.06 0.05 0.04 Interpixel (1x) 0.03 0.02 0.01 0 - - - - - 100 80 60 40 20 0 Voltage (V) • Strong dependance of inter-pixel capacitance on trench dimension • Minor dependence of back-plane capacitance on trench dimension
ULITIMA, 12 Sept. 2018 G.-F. Dalla Betta 22 Simulated capacitance (2): interpixel fit Thin metal poly Capacitance vs Trench length - ´ 15 10 45 Capacitance (F) Simulated Capacitance Calculated Capacitance 40 Interpixel capacitance fitted with simple parallel-plate capacitor model, 35 with gap d ! = # $ # %& 30 ( ) *++ ' 25 20 ) *++ (-./) = 179056 7 15 40 42 44 46 48 50 µ Trench Length ( m)
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