How to design a good sensor? General sensor desing rules Avoid high electric fields Provide good interstrip isolation (high Rint) Avoid signal coupling to neighbour (low Cint) Available tuning parameters: – w/p ratio (strip width at pitch 90µm) – P-stop placement – P-stop doping – P-spray concentration

P-stop design rules S tr ip P-stop Strip distance width Electric field dependent on p-stop distance to strip Lower fields for large distance to strip E-field dependent on p-stop width Small width shows lower electric fields FZ320P

High implant depth and high p-spray doping produce high electric fields at the strip edge Too low p-spray doping does not isolate the strip at higher oxide charge Tuning difficult Electric Fields – p-spray before irradiation

Interstrip Capacitance Higher interstrip capacitances for higher w/p ratio at pitch 90µm Higher electric fields for larger w/p ratio (backup)

5 Pstop-5e15cm -3 Pstop-5e16cm -3 Pstop-5e17cm -3 Rint (ohm) Strip pitch : 90 micron (width = 20 micron) Fluence: 1e15cm -3 Effect of P-stop doping concentration : Rint Pstop – 5e17cm -3 Pstop 5e15cm -3 Bias = 200V QF = 1.5e12cm -2 E field (V/cm) - Higher p-stop doping  Higher Rint but lower breakdown voltage -Higher Pstop doping leads to very high E field at lower biases near Pstop curvature which can lead to sensor breakdown or probably microdischarges also. - Lower Pstop-doping concentration is preferred. Interstrip resistance (irrad. Sensor) 5e+5 G M E-field at 0.1µm below SiO2

Effect of P-stop doping width : Rint - Rint and E-field independent of single p-stop width - Strip pitch : 90 micron (width = 20 micron) - Single Pstop (14µm and 28µm ); Pstop doping conc. = 5x10 16 cm -3 - Fluence = 1e15cm -3 P-stop 9 E (V/cm) Rint (Ohm) 6

Summary Sensor Design Lower electric fields for larger pitch/width ratio Large w/p is negative for Cint Pitch 90µm, Strip width 20µm is a good configuration P-spray isolation: – P-spray doping depth should be shallow for low electric fields – P-spray doping difficult to tune P-stop placement: – Lower fields for smaller width of p-stop – Placements of p-stop should be in the center of the strips – P-stop doping concentration should be larger than 5e15cm-3 to isolate – High p-stop doping leads to high electric fields after irradiation (microsdischarges and breakdown)

Backup

Electric Fields – n-bulk before irradiation Qox=1e11cm-2, V=1000V Comparing (p90,w20), (p240,w20), (p240,w60), (p90,w60) 2 cut lines: 0.1µm and 1.3µm below SiO2 (p90,w60) not converging (too high fields) Highest fields for very small width/pitch Higher electric fields at the junction in the silicon bulk (at 1.3µm)