single-photon avalanche diodes (spads) demystified

1FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

SINGLE-PHOTON AVALANCHE DIODE

DEMYSTIFIED

Fabrizio Guerrieri

2FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

LET’S CONSIDER THE TYPICAL PN JUNCTION I-V CHARACTERISTICS…

3FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

AVALANCHE CURRENT(JUNCTION BREAKDOWN)

DIRECT CURRENT

INVERSE CURRENT DUE TO THERMAL GENERATION IN THE DEPLETED ZONE

PN JUNCTION

4FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

AVALANCHE CURRENT(JUNCTION BREAKDOWN)

DIRECT CURRENT

INVERSE CURRENT DUE TO THERMAL GENERATION IN THE DEPLETED ZONE

PN JUNCTION

THE SPAD WORKS HERE

5FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

HOW DOES A SPAD WORK?

6FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

WITH A REVERSE VOLTAGE BELOWBREAKDOWN NO CURRENT FLOWS

7FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

8FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

AT THE BEGINNING,

NO CURRENT FLOWS EVEN WITH A REVERSE VOLTAGE ABOVE BREAKDOWN

9FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

10FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

AN AVALANCHE CURRENT IS TRIGGERED BY THEFIRST PHOTON GENERATING AN ELECTRON/HOLE

PAIR IN THE DEPLETED REGION

11FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

12FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

THE BRANCHED CHARACTERISTIC OF A SPAD

13FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

OBVIOUSLY A FRONT-END CIRCUIT (WE CALL ITQUENCHING CIRCUIT) IS NEEDED IN ORDER TO:

1. ENABLE THE SPAD RISING THE REVERSE VOLTAGE ABOVE BREAKDOWN

2. DETECT THE AVALANCHE CURRENT

3. QUENCH THE AVALANCHE CURRENT LOWERING THE REVERSE VOLTAGE BELOW BREAKDOWN

14FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

TWO MAIN ADVANTAGES

1. SINGLE-PHOTON LEVEL SENSITIVITY

2. ELECTRONIC PULSE’S RISING EDGE WITH VERY LOW TIME JITTER(30 ps OR BETTER)

HOW CAN I USE A SPAD?

15FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

1. TIME CORRELATED SINGLE-PHOTON COUNTING (TCSPC)(WE INFORMALLY CALL IT “PHOTON TIMING”)

2. TIME OF FLIGHT (TOF)

3. PHOTON-COUNTING

HOW CAN I USE A SPAD?

16FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

1 - PHOTON TIMING

17FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

1 - PHOTON TIMING

18FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

After somelaser pulses…

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

After somelaser pulses…

After morelaser pulses…

1 - PHOTON TIMING

20FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

After somelaser pulses…

After morelaser pulses…

1 - PHOTON TIMING

21FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

After somelaser pulses…

After morelaser pulses…

After MANYlaser pulses…

1 - PHOTON TIMING

22FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

2 – TIME-OF-FLIGHT

23FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

2 – TIME-OF-FLIGHT

24FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

2 – TIME-OF-FLIGHT

25FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

Laser pulse’s shapeEstimated TOF

2 – TIME-OF-FLIGHT

26FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

3 - PHOTON COUNTING

THE QUENCHING CIRCUIT DELIVERS AN OUTPUT PULSE EVERYTIME THE SPAD DETECTS A PHOTON

27FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

3 - PHOTON COUNTING

IN OUR ARRAYS EVERY PIXEL CONTAINS EVERYTHING TO DO PHOTON-COUNTING

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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