EBOOK Autonomous Vehicle Engineering Guide Top Breakthroughs & Resources in Autonomous and Connected Vehicles AUTONOMOUS VEHICLE ENGINEERING GUIDE 5 Contents SENSORS 7 3 For Lidar, MEMs the Word 5 New Performance Metrics for Lidar 7 Detecting Pedestrians SOFTWARE AND AI/MACHINE LEARNING 12 9 Software Building Blocks for AV Systems 12 New Mobility’s Mega Mappers 15 Can Autonomous Vehicles Make the Right ‘Decision?’ 19 CONNECTED VEHICLE ELECTRONICS 17 Expanding the Role of FPGAs 19 Electronic Architectures Get Smart ABOUT ON THE COVER Autonomous Vehicle Engineering covers the In the article Software Building Blocks constantly-evolving field of autonomous and for AV Systems, Sebastian Klaas explores connected vehicles from end to end — covering how Elektrobit's unique software frame- key technologies and applications including work is designed to smooth develop- sensor fusion, artificial intelligence, smart cities, ment of automated driving functions. and much more. This Autonomous Vehicle Automated valet parking is an example Engineering Ebook is a compilation of some of of a practical application of the software the magazine's top feature articles from thought framework. Read more on page 9. leaders, and is your guide to designing the next (Image: Elektrobit) generation of vehicles. 2 AUTONOMOUS VEHICLE ENGINEERING SAE EBOOK SENSORS For Lidar, MEMS the Word by Charles Chung, Ph.D. Tiny gimballed mirrors on chips are being developed that could improve the form factor and cost of automotive lidar. As automakers and their technology partners develop lidar sensors to enable SAE Level 4-5 autonomous driving, some systems designers believe MEMS micromirrors have the potential to reduce overall size and cost—two major hurdles to widespread lidar adoption. A basic lidar includes a light source, a scanning mirror, and a light receiver. While the light source and the light detectors use semicon- ductor components, scanning of light still relies on traditionally man- ufactured scanning or rotating mirrors, which are often the bulkiest and costliest lidar component. MEMS—an acronym for micro-electro-mechanical systems—is a Charles Chung A typical MEMS micromirror system is composed of the silicon micromirror chip, ASIC type of semiconductor device incorporating non-electronic compo- (Application Specific Integrated Circuit) electronics to actuate and control the mirror, the nents. They are used in a plethora of product applications. Automo- package that protects the micromirror and ASIC, and software. biles are rich with MEMS devices—new vehicles typically include over 30 MEMS chips. MEMS devices are included in accelerometers for simultaneous needs: a large (2-4-mm) micromirror, with a wide (30- airbag deployment, gas sensors for engine monitoring, pressure sen- 60-degrees) angular range of motion, that can pass rigorous auto- sors for tire pressure monitoring, yaw-rate sensors for vehicle stability motive testing and validation. control, and many more. Typical development times and costs for a new custom MEMS de- In the MEMS lidar application, a tiny mirror directs a fixed laser vice are 18-24 months and $1 million to $3 million to a final prototype. beam in multiple directions. The micromirror, moving rapidly due to To reach full production, it typically takes three to five years and $10 its low moment of inertia, can execute a two-dimensional scan in a million to $20 million, experts explain. fraction of a second. It can replace the traditional lidar’s bulky scan- Validating MEMS micromirrors for automotive includes, as SAE ning component with a chip that measures about 5-mm square and readers know, meeting many durability and reliability requirements costs on the order of dollars to tens of dollars, developers claim. dictated by established standards, such as the AEC-Q100. These in- clude vibration, temperature, humidity, electrical shock, mechanical In search of a new chip shock, and chemical resistance. Moreover, the volume of chips is ap- The ideal MEMS micromirror for lidar is still in development. Exist- proximately 100M per year, with the quality level at parts-per-million ing micromirrors were designed for other applications, such as pro- (or lower). jection displays or optical switching. They lack lidar’s three Micromirrors have been in commercial production for more than 20 years. The most development has been in optical switching and displays. Among displays, there are two types, digital and analog. Digital mirrors switch between only two positions. Analog mirrors have a continuous set of positions. Analog micromirrors for displays bear the closest resemblance to lidar micromirrors. Like lidar, these MEMS micromirrors have a single mirror that moves in analog fashion in two directions. But, the mirror is smaller (<1 mm) than those typically used in lidar. And perhaps most importantly, display micromirrors were typically engineered for consumer applications, whose qualification requirements are less challenging than for automotive. Design challenges There are a multitude of design implications of the increased mirror Lawrence Livermore National Laboratory LLNL-JRNL-702806 National Laboratory Livermore Lawrence size and automotive qualification requirements. Automotive tempera- A hexagonal MEMS micromirror measuring approximately 0.5 mm per side. ture ranges are wide (-40°C to +150°C), and mismatches in the coeffi- AUTONOMOUS VEHICLE ENGINEERING SAE EBOOK 3 SENSORS Electronics and software communicate with the system and mon- itor and control the mirror. The electronics are typically embodied in the ASIC (Application Specific Integrated Circuit) and are packaged together with the MEMS chip. The ASIC is mixed-signal and has a digital portion for programmable command and communication with the system and an analog section for direct control and readout of the mirror. The ASIC needs to be engineered for automotive qualification to tolerate adverse conditions such as water intrusion, electrical shock, and electromagnetic engine noise. MEMS lidar packaging and test After silicon chips are fabricated, they are placed into “packaging” that protects the chip from the environment, while allowing electrical and optical signals to pass to and from the MEMS micromirror. The packaging is a critical part of all MEMS devices, particularly so for au- tomotive applications, since it will protect the MEMS device from water, dirt, oil, particles, and other contaminants that can cause the device to fail. While the packaging protects the MEMS chip, it can also adversely Charles Chung affect the chip. Many MEMS device failures are associated with the Typical micromirror chip with mirror on two gimbals (torsional springs) that enable rota- tion about the X and Y axes. An actuator is typically integrated underneath the mirror to packaging. For example, packages are typically made of ceramic, avoid interference with the light. metal, and/or plastic, and over an automobile’s wide temperature range there can be a strong CTE mismatch between the package and cient of thermal expansion (CTE) are a common source of device fail- the silicon chip. This can cause inaccuracies, errors, and outright fail- ure. This implies that a mirror which is composed of a single material, ures. such as silicon, will have the lowest failure rates due to CTE mismatch. Ceramic packages have the closest CTE match to silicon but are Mechanical shock and vibrational requirements require that the the most expensive. Plastic packages are the most cost effective but gimbal designs be able to withstand high forces, reject motion in the have the largest CTE mismatch and cannot hermetically protect the unwanted translational and rotational directions, while being pliable MEMS device. The cost sensitivity of consumer applications requires enough to rotate about the desired directions. that they use plastic packaging, and many of the techniques used in Automotive humidity requirements require that the device tolerate those applications can be adapted to manage the CTE mismatch for 0% to 100% humidity. One implication is that the device must tolerate automotive applications. water droplets. A common cause of failure in MEMS devices is “stic- After the chip is packaged, the device is calibrated and tested to tion,” which occurs when the moving parts of a MEMS device stick to ensure that it meets requirements. With approximately 100 million the stationary parts. When this happens, the moving parts can no automobiles produced every year, testing every device is time con- longer move, and the MEMS device no longer functions. suming and costly. As a result, efficient testing requires a strategy The surface tension of a water droplet can bridge small gaps in the that tests devices at multiple points in the manufacturing process, as MEMS chips. As the water droplet evaporates, it draws together the well as custom test capabilities that can evaluate every device effi- two sides of the gap, stick them together, and the micromirror is un- ciently. ■ able to scan. To prevent this, one method is to avoid small gaps in the design, which electrostatic actuation typically requires. Another Charles Chung, Ph.D., has over 25 years of experience with MEMS devices and method is to reduce the droplet’s surface tension with a chemical microsystems. He is a member of the University of Pennsylvania’s Singh Nan- otechnology Center’s Advisory Board, and a recipient of the Gates Global Grand treatment often used in MEMS microphones. Hermetic packaging is Challenges Grant. He has developed multiple MEMS devices, including