Silicon Detectors for the VELO Upgrade G. Casse University of Liverpool 1 VELO Upgrade Nikhef Nov

Planar Silicon Sensor issues: Planar silicon or else? Radiation tolerance. Limit of planar silicon sensors 2 VELO Upgrade Nikhef Nov Pros:  Well known technology with standard processing  Many commercial suppliers including those capable of delivering the orders  High yield and relatively lost cost (particularly if single-sided n-in-p)  Long experience with sensor design and optimization  Processing of thinned detectors established with commercial suppliers  Minimum ionising particle charge collection studied after doses to 2×10 16 n eq /cm 2 Cons:  Lower signal for a given leakage current/power consumption than other technologies  Highest dose regions might require lower electronics threshold  Lower temperatures required for highest does regions than other technologies  Highest dose regions require higher voltages than other technologies  Edgeless detector designs requires a non-planar technological step  Signals at highest doses look to rely on multiplication effects which are still poorly understood

VELO Upgrade Nikhef Nov Detector power dissipation and signal Fluence (10 15 n eq cm -2 ) Power (mW/cm 2 ) at -25 o C (no annealing) Power (mW/cm 2 ) at -25 o C (45d RT annealing) Signal (ke) 500 V1000 V500 V1000 V >10/ > 7/ / / / /216>6/ /65300/ /39180/400>4/5.5 Fluence (10 15 n eq cm -2 ) Power (mW/cm 2 ) at -50 o C (no annealing) Signal (ke) 500 V1000 V 53.1/ /20>10/ ~10 Sensor thickness: Black: 300µm Red: 140µm

VELO Upgrade Nikhef Nov Reverse current after various doses: expectations and measurements Expectations: bulk generated current, proportional to , the generation volume defined as the fully depleted fraction of the sensor. I R =  ×  ×V V FD : 5E 14 n eq cm -2 ~ 500V 1E 15 n eq cm -2 ~ 1000V 5E 15 n eq cm -2 ~ 5000V 1E 16 n eq cm -2 ~ 10000V 2E 16 n eq cm -2 ~ 20000V

Planar Silicon Sensor issues: Planar silicon or else? Radiation tolerance. Limit of planar silicon sensors Advantages of planar silicon sensors Optimising thickness. 5 VELO Upgrade Nikhef Nov

6 CCE (n-in-p) at various fluences, and comparison  m thick sensors after 1 and 2x10 16 n eq cm -2.

Planar Silicon Sensor issues: Planar silicon or else? Radiation tolerance. Limit of planar silicon sensors Advantages of planar silicon sensors Optimising thickness. Anything to win with other Silicon crystals? 7 VELO Upgrade Nikhef Nov

Material Comparison 8 After ~5×10 14 n cm -2, n-in-n FZ, n-in-p FZ, n- in-p MCz very similar At higher voltage n- in-n MCz superior up to maximum fluence (10 15 n cm -2 ) – Need higher fluence data to determine if this continues p-in-n shows inferior performance as expected 900 V Appears once trapping dominates, all n-strip readout choices studied are the same after neutron irradiation VELO Upgrade Nikhef Nov

Planar Silicon Sensor issues: Planar silicon or else? Radiation tolerance. Limit of planar silicon sensors Advantages of planar silicon sensors Optimising thickness. Anything to win with other Silicon crystals? The radiation tolerance R&D will be focused to obtained the sufficient signal at lower bias voltages and possibly for less power dissipation. Follow the charge multiplication R&D: other parameters besides thickness? Crucial aspects: services (HV and cooling -> module design). Running scenario: optimise annealing (reduce current and improve signal). 9 VELO Upgrade Nikhef Nov

10 What geometry? Do we need a Vespa? …. maybe a faster VELO could do!!

11 … where the faster VELO could be our existing geometry with improvement on the read-out. Detector could be the same, but the read-out speed and early intelligence in data processing could be much improved. The obvious advantage would be the small number of channels. Would resolution be sufficient and at what point (luminosity) the occupancy will kill the efficiency?

12 VESPA 50cc … short strip approach, where the strips of the existing R and Phi detectors are segmented (strip number*3/4). This would require a big effort in routing, would not lead to a better resolution, would keep occupancy low. Still back to back detectors would be required, signal to noise improved due to the smaller cell size (lower input capacitance to the electronics).

13 VESPA 125cc … strixel approach, where the pixel dimensions could be in the order of 50µmx µm. Large number of channels, for the required resolution probably still need R and Phi back to back detectors, difficult read-out routing (need for 3-d integration techniques). Good S/N, low occupancy.

14 VESPA 250cc … wedge-xel approach, where the pixel dimensions change with radius. Very problematic routing and positioning of the electronics if the pixel density is high (the dimension of the electronics chip is decoupled from the dimensions of the sensor), but the dimensions of the wedged-shape pixels should be such that 2-d information is delivered by one detector. Good S/N, low occupancy.

15 …or, if you need more power ….. Full square hybrid pixel design (BTev, with flip- chip electronics bump bonded to the sensors (or new soldering technologies), the size you like (probably in the future will be possible to go below 25µm diameter contacts). Hi resolution achievable, low occupancy and S/N. huge number of channels.

Planar Silicon Sensors: Geometry Pixel or microstrip? Pixels: possible one detector plane/station. High density (what will be the minimum pixel size in a few years? Micro-connectivity to ASICs?), trading between channel number/point resolution. One plane -> square pixels: advantages in changing pixel dimensions with radius? Tessellation: size of a module limited (at least in one dimension) by the reticule size of the electronics. Need for 2-4 detector tiles for covering the area. Issue of dead area at sensor ends (GR+dead silicon). Slim edge planar sensors to be developed. Nonetheless, evolution in the electronics (3-D, interconnectivity and TSV) could help significantly and the need for slim edges could be confine to the sensor outer edge (with electronics ASIC tiling a single silicon pixel sensor). Microstrips: two detector planes per station. Possible high resolution with reduced number of channels (with strip pitch <50  m). Individual channel size (strip length) dictated by occupancy. Complicated routing is anticipated. One sensor to cover the area, no need for tiling. 16 VELO Upgrade Nikhef Nov

Planar Silicon Sensors R&D Alternative Silicon crystal material (to high-res FZ n or p-type)(nMCz, duration 6 months, not essential). Double sided processing, GR and slim edge (duration 18 months, important for both pixels and microstrips). Thickness optimisation: several issues, signal, cost and mechanics (24 months, important, possibly in conjunctions with junction geometry studies). Charge multiplication: follow RD50 developments/do own research. Required bias and cooling: power predictions (reverse current) not easily extrapolated. Direct tests required, need to keep safe margin. Pixels: possible one detector plane/station. High density, trading between channel number/point resolution. One plane -> square pixels: advantages in changing pixel dimensions with radius? This research implies cutting edge activities in conjunction with ASICS/post processing manufacturers, interconnectivity issues. Microstrips: two detector planes per station. Possible high resolution with reduced number of channels (with strip pitch <50  m). Individual channel size (strip length) dictated by occupancy. Complicated routing is anticipated. 17 VELO Upgrade Nikhef Nov

A few spare slides VELO Upgrade Nikhef Nov

VELO Upgrade Nikhef Nov “Fine step” Annealing of the colleted charge, HPK FZ n-in-p, 1E15 n cm -2 Neutron irradiations in Ljubljana, neutrons are dominating the radiation damage > 25 cm radius.

VELO Upgrade Nikhef Nov “Fine step” CCE Annealing 1.5E16 n cm -2 Noise is the sum in quadrature of shot noise and parallel noise (taken from the Beetle chip specs, and estimated as 650ENC) Irradiated with 26MeV protons (Karlsruhe).

VELO Upgrade Nikhef Nov nnealing of the reverse current, Micron n-in-p, after 1.5E16 n eq cm -2 (26 MeV p irradiation)

VELO Upgrade Nikhef Nov Effect of trapping on the Charge Collection Distance After heavy irradiation it seems that the V FD is lower than expected from extrapolation from lower doses. This could yield a larger signal. But, is depletion the limiting factor after heavy irradiation? Q tc  Q 0 exp(-t c /  tr ), 1/  tr = . v sat,e x  tr = av G. Kramberger et al., NIMA 476(2002),  e =  cm -2 /ns  h =  cm -2 /ns In fact, the charge trapping at radiation induced defect centres has a larger effect on the signal. The collection distance at saturation velocity: av after 1x10 15 n eq cm -2 : 240µm (expected charge ~19ke). av after 5x10 15 n eq cm -2 : 50µm (expected charge <4ke). av after 1x10 16 n eq cm -2 : 25µm (expected charge <1.3ke). av after 2x10 16 n eq cm -2 : 12µm (expected charge <1ke). Expected signal from charge trapping

23 Moreover there is clear indication of a charge multiplication mechanism after irradiation. A rather marginal improvement of the CCE is found by going from -25 o C to -50 o C. But there is substantial evidence of charge multiplication. 140 and 300  m n-in-p Micron sensors after 5x10 15 n eq 26MeV p VELO Upgrade Nikhef Nov

G. Casse, VELO Spares and Upgrade, Ness Gardens, Oct Possible solutions to an optimised cell layout can come from recent developments

G. Casse, VELO Spares and Upgrade, Ness Gardens, Oct )Sensor wafer 2) Add dielectric and open vias 3)Add metal layers and pattern 4) Dice sensor 5) Flip-chip ASICs 6)Wirebond to hybrid Part of MCM-D? Possible solutions?