cmos spads for lidar applications - ait · cmos spads for lidar applications ... extending the...
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Werner Brockherde Fraunhofer IMS, Duisburg
CMOS SPADs for LIDAR Applications
AIT Scientific Vision Days November 9th, 2016
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Outline
Introduction to Fraunhofer IMS
Single Photon Avalanche Diodes in CMOS
Examples of CMOS SPAD Applications
SPAD für LIDAR
Design example
Summary
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FRAUNHOFER IMS
Microelectronic Circuits and Systems, Duisburg
Director: Prof. Dr. rer. nat. Anton Grabmaier
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Fraunhofer IMS
Technology & Devices
ASICs CMOS Imagers
Ambient Intelligent Systems
Wireless Transponder
Systems
Biohybrid Systems
Pressure Sensors
Chip Design
CMOS Wafer Fab
Assembly & Test
IR Imagers
CMOS Process
Power MOS / Smart Power
High Temperature µ-Electronics
640 x 480 IRFPA (Uncooled α-Si)
Infrared Thermographie
25µm Bolometer (SEM-Image)
1D and 2D CMOS Image Sensors
Pressure Sensors
3D CMOS Image Sensor
3D Cam Scheme
Medical Implants
Pressure Sensor Systems
Nanopotentiostate
Glucose and Lactate Sensors
Bio Sensors
Embedded Systems
inBad
µ-Transponder System
Hospital Engineering
Wireless Sensor Networks/ZigBee
Embedded IP-Net- works & Middleware
Business Fields
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Fraunhofer IMS
Total area: 1300 m2
Clean room class: 10
Wafer size: 200 mm (8 inch; 0.35 µm)
Staff: working in 4 shifts / 7 days a week
Capacity: > 50.000 Wafer p.a.
Excellence of the CMOS-Line
Complete CMOS process line plus integrated sensors (SOI, imager, pressure, mixed signal)
ICs from a few 100 ASICs to few million
Infrastructure - CMOS Fab
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Fraunhofer IMS
Total area: 600 m²
Clean room class: 10
Wafer size: 200 mm
Miss ion
Extending the application areas of CMOS (“More than Moore”) by post processing on CMOS wafers.
Development Activ ities
Adding layers, structures, devices onto preprocessed “intelligent substrates” (CMOS wafers) to create integrated sensor systems.
Examples: micro bolometer arrays for IR imaging, biosensors, opto sensors.
Infrastructure - Microsystems Lab&Fab
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Infrastructure IMS
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Business Field: CMOS Image Sensors
Werner Brockherde
FRAUNHOFER IMS
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Service and Know-how - Optical CMOS Sensors
In the field of „Optical CMOS Sensors” Fraunhofer IMS is providing:
Serv ice and Support
Design of customized image sensors and dedicated optical sensors
Wafer fabrication in Fraunhofer IMS fab (L035-OPTO) or foundries
Electro-optical test on wafer and device level
Device qualification
Full service from design to fabrication
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Example Project – RGB Line-Scan Sensor
Design and Development
Designed for high speed surface inspection
Unique Selling Points
2048 x 60 pixels
600 kHz (b/w) / 200 kHz (RGB) line rate world record!
RGB pixel with 100% fill factor
Column-parallel 10 bit ADCs
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Service and Know-how - Optoelectronic Devices
In the field of „Optoelectronic Devices” Fraunhofer IMS is providing:
Serv ice and Support
Development of novel optoelectronic devices
Use of standard CMOS processes: 0.5µm, 0.35µm, and foundry processes
Device modeling and optimization with advanced simulation tools
Characterization of „test inserts“ to extract and monitor device parameters (capacitance, dark current, spectral response, etc.)
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Technology - CMOS 0.35µm Process “Opto”
The IMS 0.35µm CMOS process “Opto” is providing: Opto Process Features Stitching
Planarization
UV transparent silicon nitride passivation
Salicide-blocking
Color filter deposition & microlenses
Opto Devices
Pinned photodiodes (low noise, low dark current)
High temperature photodiodes
Lateral Drift-Field Photodetectors (LDPD)
Single-Photon Avalanche Diodes (SPADs)
Embedded CCD
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© Fraunhofer IMS P
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SPAD Operating Principle
Single-Photon-Avalanche-Diode (SPAD) is an avalanche photodiode operated above breakdown voltage (= Geiger-Mode)
Very few photons can be detected
Fast operation with good time resolution
IV characteristic of APD
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Characteristics of SPADs in IMS 0.35µm CMOS Process
SPAD characteristics (30 µm active area)
Dark count rate (DCR) < 50 cps at room temperature
Timing response < 140 ps FWHM
Uniformity 95% of pixels have close to avg. DCR
Breakdown voltage (VBD) 26 V
Temperature drift of VBD 37.8 mV/K
Afterpulsing probability < 1% at dead time > 50 ns
Pixel pitch As low as 10 µm
Spectral range 300 nm – 1000 nm
Dynamic range 106 dB
Noise-equivalent Irradiance @ 905 nm 11 pW/cm²
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BackSPADs
Schematic cross section of backside illuminated SPAD
sensor after integration
Radiation ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
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SPAD Linear Sensor Technology: 0.35µm Standard CMOS Prozess
2×128 SPAD-pixel
3.3V Digital output and control
60% Fillfactor @20µm pixel pitch
Applications:
Time-resolved spectroscopy (e.g. Raman spectroscopy)
ToF/LIDAR (with adaption of readout electronics)
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IMS design examples: Silicon Photomultiplier (SiPM)
20×20 SPAD-elements on 1×1 mm² active area
Geometric fillfactor: 68% @ 50µm pitch
Applications:
Detector in high-energy particle physics
Scanning-LIDAR
PET-detector (medicine)
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Time-of-Flight methods
Direct
Direct time measurement
Jitter is limiting precision
High optical power density in short pulses
Complex analog circuitry (TDC)
High precision possible
Indirect
Calculation of distance from # photons
Photon statistics limits precision
Lower optical power density
Digital circuitry (counters)
Dead time limits counting rate
Laser
Ob
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Sensor
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LIDAR-Methods - Benchmarking
Scanning LIDAR
Subsequent pointing to object area points
Only one object point at a time
Mechanical scan
High optical power density
High distance range
Single detector element
Low framerate
Flash LIDAR
Complete scene is take in a flash
Solid state solution possible
No moving parts
Low optical power density
Low distance range
Detector array required
High Framerate
CameraCamera
Target Scene Target Scene
CameraCamera
Target Scene Target Scene
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Challenges for Automotive LIDAR
Background light suppression
20…40 klux are realistic
For short ranges120 klux seem possible
Limits for Flash LIDAR
For long ranges flash LIDAR is not very efficient
Trade-off: laser power / range / FOV
Long ranges are covered with video and radar
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Example of Flash LIDAR SPAD linear sensor for ADAS
Pedstrian detection
Parking Assistance
Flash LIDAR-System with 3 SPAD line sensors for short and medium ranges
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Approach: Detection of target area by 4 lines
Detector allows high fillfactor
Example of Flash LIDAR
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SPADs in CMOS Technology allows for highly efficient LIDAR sensors
Backgroung light suppression is still an issue in outdoor applications
New signal processing methods and algorithms enable extension of dynamic range
Summary