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Simulation of new P-type strip detectors with trench to enhance the charge multiplication effect in the n-type electrodes. G. Pellegrini , J. P. Balbuena, C. Fleta, P. Fernández-Martínez, D. Quirion, S. Hidalgo, D. Flores, M. Lozano Centro Nacional de Microelectrónica (IMB-CNM-CSIC)

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slide1

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

G. Pellegrini, J. P. Balbuena, C. Fleta, P. Fernández-Martínez, D. Quirion, S. Hidalgo, D. Flores, M. Lozano

Centro Nacional de Microelectrónica (IMB-CNM-CSIC)

G. Casse, D. Forshaw

Liverpool University

Work partially supported by RD50 collaboration

slide2

Introduction

  • 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 significantly
    • Higher capacitance  Higher noise
slide3

Technological proposals

  • 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+

8µm

5µm

5µm

p-stop

32µm

20µm

285µm

p-

p+

slide4

Technological proposals

  • 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+

8µm

5µm

p-stop

32µm

20µm

285µm

p-

p+

simulation model
Simulation Model

Sentaurus ISE-TCAD

  • Impact Ionization Model: Universty of Bolonia
  • Irradiation trap model:
  • Acceptor; E= Ec + 0.46 eV; η=0.9; σe = 5 x 10-15; σh = 5 x 10-14
  • Acceptor; E= Ec + 0.42 eV; η=1.613; σe = 2 x 10-15; σh = 2 x 10-14
  • Acceptor; E= Ec + 0.10 eV; η=100; σe = 2 x 10-15; σh = 2.5 x 10-15
  • Donor; E= Ev - 0.36 eV; η=0.9; σe = 2.5 x 10-14; σh = 2.5 x 10-15
slide6

Simulation of the Electric Field

Strip Detector

Poly Trench

P diffusion

High Electric Field region driven deep in the bulk

High Electric Field peak at the centre of the strip

slide7

Simulation of the Electric Field

High Electric Field peak at the junction

Curves at 500 V

No Irradiated

Irradiated. Φeq = 1 x 1016

High Electric Field region driven deep in the bulk

slide8

Simulation of the Capacitance

n+

CInterStrip

p-

CBulk

p+

Increment related with the depletion of the P diffusion

Once Fully Depleted, the bulk capacitance is the same for all the structures

  • We need experimental results to extract any conclusion
slide9

Variation over the basic proposals

  • 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

n+

5µm

8µm

5µm

p-stop

32µm

20µm

285µm

P-type diffusion

p-

p+

slide10

Variation over the basic proposals

  • Large P-Type covering all the strip width
    • N+/ P-type diffusion junction creates a high electric field region  multiplication

80µm

32µm

20µm

n+

8µm

30µm

p-stop

P-type diffusion

285µm

p-

p+

slide11

Variation over the basic proposals

  • 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
      • It should work after irradiation

n+

Premature Cylindrical Breakdown

p-

p+

slide12

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
  • Devices with large 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

Fabrication: step 50 out of 80. Doping trenches.

slide13

Status of the Work: PAD Diodes

N+

  • 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

P

385 mm

5000 µm

  • First Measurements: Gain ~2

5000 µm

slide14

Conclusions and Applications

  • We have shown several new designs to enhance the multiplication process.
  • If detector will work many tests must be done: uniformity, stability, reproducibility etc.....
  • A PAD detector with small gain has been fabricated following some of the procedures described in this work.
  • A run containing the discussed designs is being fabricated for subsequent characterisation.
  • Test uniformity with test beam or laser with Alibava
  • Applications:
    • - Radiation Hard Detectors
    • - Tracking Detectors
    • - Charge multiplication permits the fabrication of thinner detectors