Simulation of new P-type strip detectors with trench to enhance the charge multiplication effect in the n- type electrodes

Transcription

1 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Simulation of new P-type strip detectors with trench to enhance the charge multiplication effect in the n- type electrodes P. Fernández-Martínez, G. Pellegrini, J. P. Balbuena, D. Quirion, S. Hidalgo, D. Flores, M. Lozano (IMB-CNM-CSIC) G. Casse Liverpool University Work partially supported by RD50 collaboration

2 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Introduction a. Irradiated detectors suffer displacement damage that change their charge collection dynamics Defects induced by radiation increase the electric field at the junction of the N + diffusion The electric field increase leads to a multiplication of the collected charge in irradiated devices b. Project: fabricate a p-type strip detector with small gain Similar signal before and after irradiation Multiplication occurs at low bias voltage Gain should be limited between 2 and 10: - Avoid Crosstalk - Avoid exceeding the dynamic range of readout electronics Capacitance should not increase - Higher capacitance Higher noise

3 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Technological proposals I. Trench filled with doped polysilicon along the centre of the strip pitch A N + contact is created into the silicon bulk that modifies the electric field in the collection region multiplication 80µm Poly trench n+ 5µm 5µm 8µm p-stop 285µm 32µm 20µm p- p+

4 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Technological proposals II. P-type diffusion along the centre of the strip pitch Under reverse bias conditions, a high electric field region is created at the N + P junction multiplication 80µm P-type diffusion n+ 285µm 5µm 32µm 8µm 20µm p-stop p- p+

5 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Strip Detector Simulation of the Electric Field Poly Trench P diffusion High Electric Field region driven deep in the bulk High Electric Field peak at the centre of the strip

6 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 High Electric Field peak at the junction Simulation of the Electric Field Electric Field (V/cm) High Electric Field region driven deep in the bulk Strip Center Depth (µm) Strip Poly Trench P Diffusion Achieved Electric Field values are comparable with the irradiated devices Electric Field (V/cm) Strip Detector: Strip Center No Irradiated Φ eq = 1 x n/cm Depth (µm)

7 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Simulation of charge collection: MIP Strip Detector Poly Trench P Diffusion A/cm 2 We We are are developing developing a simulation simulation procedure procedure to to obtain obtain the the gain gain value value

8 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Simulation of the Capacitance n+ p- p+ C Bulk C InterStrip C Inter_Strip (pf) Strip Poly Trench P Diffusion Applied Voltage (V) Bulk Capacitance (pf) Strip Poly Trench P Diffusion Applied Voltage (V) Once Fully Depleted, the bulk capacitance is the same for all the structures Increment related with the depletion of the P diffusion We need experimental results to to extract any conclusion

9 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Variation over the basic proposals I. P type diffusion, implanted through a trench filled with oxide, along the centre of the strip pitch N + / P-type diffusion junction creates a high electric field region multiplication 80µm Oxide trench 285µm 5µm n+ 5µm 32µm 8µm 20µm p-stop P-type diffusion p- p+

10 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Electric Field Variation over the basic proposals Charge Collection 100 C Bulk (pf) Strip Oxide Trench Anode Voltage (V) The deeper the trench, the larger the volume of multiplication - We are considering trenches of different depth

11 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Variation over the basic proposals II. Large P-Type covering all the strip width N + / P-type diffusion junction creates a high electric field region multiplication 80µm 32µm 20µm n+ 30µm 8µm p-stop 285µm P-type diffusion p- p+

12 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Variation over the basic proposals n+ DRAWBACK: If N + and P diffusions are performed with the same mask, a premature breakdown is expected due to the curvature of the junction - N + diffusion should overlap P diffusion One extra level of Mask Optimisation of the overlap size Premature Cylindrical Breakdown p- p+

13 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Status of the Work: Fabrication The fabrication run includes: Conventional Strip Detectors Poly Trench structures with different trench depths: 5 µm 10 µm 50 µm Structures with small P layer along the center of the strip Oxide filled trench structures with a P layer implanted through the trench: 5 µm 10 µm 50 µm Devices with large P layer along the center of the strip

14 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Status of the Work: PAD Diodes We have fabricated PAD diodes with a P layer diffused under the N + diffusion N + / P-type diffusion junction creates a high electric field region multiplication High Electric Field region leading to multiplication N µm First Measurements: Gain ~2 P 5000 µm 5000 µm

15 Simulation of new P-Type strip detectors RESMDD 10, Florence October /15 Conclusions and Applications 1 We have presented several new designs to enhance the multiplication process. 2 Presence of trenches or diffused P layers in the strips can provide small gain values. 3 Capacitance value can be deteriorated. It will be better established with the experimental results. 4 A run containing the discussed designs is being fabricated for subsequent characterisation. 5 A PAD detector with small gain has been fabricated following some of the procedures described in this work. 6 Applications: - Radiation Hard Detectors - Tracking Detectors - Charge multiplication permits the fabrication of thinner detectors