A look inside the Single Photon Avalanche Diode (SPAD) from STMicroelectronics entering the high-end Apple handset
Today, time-of-flight (ToF) systems are among the most profitable and innovative imaging technologies. Every major consumer product manufacturer wants to integrate such devices to provide 3D imaging, proximity sensing, ambient light sensing, gesture recognition, and more. STMicroelectronics has been investigating this technology in depth, and now provides several smartphone manufacturers ToF ranging sensors. Apple’s iPhone 7 Plus goes further with a custom proximity sensor, the smallest FlightSenseTM device in STMicroelectronics ToF portfolio.
Located in the front of the phone, above the main speaker, the FlightSenseTM proximity sensor uses optical land-grid array (LGA) packaging. The custom Apple device measures 2.80 mm x 2.40 mm, half the size of the rest of STMicroelectronics’s portfolio.
This report analyzes the complete microsystem, from the illumination device, which is a Vertical-Cavity Surface-Emitting Laser (VCSEL), to the collector, which is based on STMicroelectronics’ Single Photon Avalanche Diode (SPAD). It includes a complete cost analysis and price estimation of the device based on a detailed description of the package, the ToF detector and the VCSEL.
It also features a complete technology comparison with every product in STMicroelectronics’ ToF portfolio since the first generation, including the VL53L0X and VL6180X, especially looking at the SPAD’s evolution.
Overview / Introduction
STMicroelectronics Company Profile and Time of Flight technology
Apple iPhone 7 Plus Teardown
> Physical Analysis Methodology> Package View and dimensionsPackage opening and wire bonding processPackage cross-section: adhesives, PCB, filters, FOV> VCSEL Die- View and dimensions - Wire bonding, cavity- Cross-section - Process characteristics> ASIC Die- View, dimensions and marking- Die overview: active area, SPAD technology- Die delayering, main block IDs and process- Cross-section: metal layers, SPADs- Process characteristics
Physical Comparison with VL53L0X and VL6180X
> Package, Functions, FOV, Optical Blocking Package, ASIC and VCSEL, SPADs
Manufacturing Process Flow
> Overview> ASIC Front-End Process> VCSEL Front-End Process> ASIC Wafer Fabrication Unit> VCSEL Wafer Fabrication Unit> Packaging Process Flow> Final Assembly Unit
> Cost Analysis Overview> Main Steps Used in the Economic Analysis> Yield Hypotheses> ASIC and VCSEL Die Cost- Front-end cost- Back-end: Tests and dicing- Wafer and die cost> Component- Front-end cost- Back-end: Tests and dicing- Wafer and die cost
Estimated Price Analysis
> Estimation of the Manufacturing Price
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Manufacturing process flow
Supply chain evaluation
Manufacturing cost analysis
Estimated sales price
Comparison within STMicroelectronics’ time-of-flight portfolio: - Previous generations: VL6180X and VL53L0X - Functions and SPAD evolution