Automotive
How the latest NAND Flash-based storage devices achieve high reliability in high- temperature automotive applications
By Jason Chien, embedded storage product marketing director, Silicon Motion W
ith the introduction of every new generation of passenger vehicle, the automation, safety and navigation systems
become more sophisticated. Supported by an array of cameras, radar (RF) and LiDAR (optical) ranging systems, sensors, and other detection systems, Advanced Driver Assistance Systems (ADAS) generate and process huge quantities of digital data. Infotainment systems, too, are growing in code size as drivers demand superior navigation and information systems, and passengers look for more entertainment options in the front and rear of the cabin. In functional terms, the car is becoming a data centre on wheels – and like a data centre, it needs high-speed access to a large data storage capacity. Reliability concerns have led automotive manufacturers to end the use of traditional Hard Disk Drive (HDD) storage devices, which offer a limited lifetime and are prone to mechanical failure.
Instead, automotive system designers today prefer to use a mass storage device which is based on NAND Flash memory technology, such as a Solid-State Disk (SSD), eMMC drive or UFS (Universal Flash Storage) device. NAND Flash has become the preferred technology for mass storage in mobile phones, laptop computers and other consumer devices as well as in SSDs because it offers a valuable combination of high memory density and high performance. This means that huge data storage capacity can be provided in a small packaged device, and the user benefits from rapid access to stored data and quick data storage operations.
These characteristics are important as well to automotive manufacturers. But automotive applications impose special requirements which raise important additional questions about manufacturers’ choice of NAND storage device:
Performance – in use cases such as driver assistance and navigation, latency is a key
14 November 2022
figure of merit. Automotive manufacturers require fast Read and Write speeds and high data throughput. Data integrity – every Read and Write operation carries a risk of generating bit errors, which can lead to data loss or corruption. Reliability is a critical factor in the automotive market, and in a storage device, data integrity is an important marker of reliability. Data retention – unlike a consumer device such as a mobile phone, a vehicle is expected to have an operating lifetime of at least ten years. Automotive manufacturers want to be confident that their chosen NAND storage device will retain data for the life of the vehicle.
In vehicles, the long-term reliability and lifetime of an electronics component such as a mass storage device are crucial criteria. The automotive industry applies strict qualification tests, according to the AEC-Q100 standard, to the integrated circuits used in automotive Electronic Control Units (ECUs), with the aim of achieving zero defects over a long lifetime at temperatures of 85°C or higher.
The goal of reducing the component defect rate to zero is important because of the long lifetime of a vehicle, the high number of components in a vehicle, and the huge cost of
Components in Electronics
rectifying a known fault in a fleet of vehicles which are in service – not to mention the reputational damage to a car maker’s brand. To illustrate the point simply, imagine a single Electronic Control Unit (ECU) consisting of 1,000 parts. If the ECU manufacturer tolerated a defect rate as low as 1ppm, this single ECU alone would be responsible for 1,000 faults in a fleet of one million vehicles. And according to a 2019 report from analyst firm IHS Markit, a new luxury vehicle can contain as many as 150 ECUs1
.
This is why the automotive industry imposes the goal of a zero-defect rate. And its strategy for reaching this goal is to apply a component qualification process, codified in the various AEC-Q10x standards. The criteria for AEC-Q100 qualification, for example, are extremely strict, and verify a component’s reliability across a number of test parameters. The main reliability tests are: n Accelerated environmental stress testing n Accelerated lifetime simulation testing n Packaging and assembly tests n Die fabrication testing n Electrical verification n Defect screening n Package integrity testing
This qualification process is exhaustive, and
has been proved to effectively screen out potentially defective parts. Components which pass the tests and achieve AEC-Q100 qualification have demonstrated a remarkably high level of reliability and integrity in a demanding set of environmental and application conditions. One of the most difficult elements of AEC-Q100 qualification for NAND Flash- based storage products to achieve is to pass the high- temperature and accelerated lifetime simulation tests. Storage systems must maintain reliable operation at continuous temperatures of up to 85°C for AEC-Q100 qualification to Grade 3, and up to 105°C for Grade 2. And the compact, chip-style packages in which the latest products, such as Silicon Motion’s Ferri family, are housed, have more constrained thermal pathways than in the larger enclosure of a typical free-standing SSD used as a computing accessory. To maintain reliable operation and data integrity in automotive storage devices, Silicon Motion applies various unique technologies which draw on its long experience in NAND Flash memory control. An understanding of these technologies will help the automotive system designer to
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