A short presentation I created during my graduate studies to explain how SPADs work and how to use them

1. 1FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
SINGLE-PHOTON AVALANCHE DIODE
DEMYSTIFIED
Fabrizio Guerrieri

2. 2FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
LET’S CONSIDER THE TYPICAL
PN JUNCTION I-V CHARACTERISTICS…

3. 3FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
AVALANCHE CURRENT
(JUNCTION BREAKDOWN)
DIRECT CURRENT
INVERSE CURRENT DUE TO THERMAL
GENERATION IN THE DEPLETED ZONE
PN JUNCTION

4. 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

5. 5FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
HOW DOES A SPAD WORK?

6. 6FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
WITH A REVERSE VOLTAGE BELOW
BREAKDOWN NO CURRENT FLOWS

7. 7FABRIZIO GUERRIERI
SPAD DEMYSTIFIED

8. 8FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
AT THE BEGINNING,
NO CURRENT FLOWS EVEN WITH
A REVERSE VOLTAGE ABOVE BREAKDOWN

9. 9FABRIZIO GUERRIERI
SPAD DEMYSTIFIED

10. 10FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
AN AVALANCHE CURRENT IS TRIGGERED BY THE
FIRST PHOTON GENERATING AN ELECTRON/HOLE
PAIR IN THE DEPLETED REGION

11. 11FABRIZIO GUERRIERI
SPAD DEMYSTIFIED

12. 12FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
THE BRANCHED CHARACTERISTIC OF A SPAD

13. 13FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
OBVIOUSLY A FRONT-END CIRCUIT (WE CALL IT
QUENCHING 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

14. 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?

15. 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?

16. 16FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
1 - PHOTON TIMING

17. 17FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
1 - PHOTON TIMING

18. 18FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
After some
laser pulses…
1 - PHOTON TIMING

19. 19FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
After some
laser pulses…
After more
laser pulses…
1 - PHOTON TIMING

20. 20FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
After some
laser pulses…
After more
laser pulses…
1 - PHOTON TIMING

21. 21FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
After some
laser pulses…
After more
laser pulses…
After MANY
laser pulses…
1 - PHOTON TIMING

22. 22FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
2 – TIME-OF-FLIGHT

23. 23FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
2 – TIME-OF-FLIGHT

24. 24FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
2 – TIME-OF-FLIGHT

25. 25FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
Laser pulse’s shape
Estimated TOF
2 – TIME-OF-FLIGHT

26. 26FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
3 - PHOTON COUNTING
THE QUENCHING CIRCUIT DELIVERS AN OUTPUT PULSE EVERYTIME
THE SPAD DETECTS A PHOTON

27. 27FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
3 - PHOTON COUNTING
IN OUR ARRAYS EVERY PIXEL CONTAINS
EVERYTHING TO DO PHOTON-COUNTING

28. 28FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
#photons

29. 29FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
#photons
FRAME
START

30. 30FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
#photons

31. 31FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
#photons

32. 32FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
#photons

33. 33FABRIZIO GUERRIERI
SPAD DEMYSTIFIED
#photons
FRAME
START
FRAME
STOP