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Date: 08-07-15

CSP packaged 1-Mbit Serial FRAM for wearable electronic devices

The microcontroller/processor inside wearable electronics devices, particularly of health and physical activity monitoring type, do multiple times of reading and writing of sensor data into the nonvolatile memory, which is now mostly a flash memory. The Flash memory has some limitation in terms of number of read/write cycles, reliability, and speed. New nonvolatile memory technology FRAM takes care of all the weaknesses in the Flash memory and fits well for wearable electronics application involving lot of data logging. FRAM also consume lot less power compared to Flash memory. FRAM has limitations in terms of memory size and so also the physical size.

The leading a FRAM semiconductor memory manufacturer Fujitsu Semiconductor could pack 1-Mbit FRAM IC in a 8-pin wafer level chip scale package (WL-CSP). The new device part numbered MB85RS1MT occupies 23% of the mounted surface area compared with the existing 8-pin small-outline package (SOP), and is roughly one-fifth as a thickness. This is the smallest 1Mbit FRAM with a serial peripheral interface (SPI) in the industry.
fram csp

Figure: Comparison of the SOP and WL-CSP Packages by volume

The suggested wearable devices by Fujitsu for this FRAM chip includes eyeglasses and head-mounted displays, medical devices, such as hearing aids and pulse meters, and activity trackers. All these devices does lot of data logging in real-time which need to be recorded on a nonvolatile memory. FRAM is highly suitable for these applications except for memory size limitations.

Compared to Flash memory' write cycles of 1 million, FRAM can work up to 10 trillion read/write cycles, that's a lot better.

The new WL-CSP measures 3.09 × 2.28 × 0.33 mm and a thickness of only 0.33 mm, so that the total mounted volume resulted in 95% less than that of the SOP.

Key Specifications
Part Number: MB85RS1MT
Density (configuration): 1 Mbit (128K × 8 bits)
Interface: serial peripheral interface (SPI)
Operating voltage: 1.8–3.6 V
Guaranteed read/write cycles: 10 trillion
Data retention: 10 years (at +85°C)
Package: 8-pin WLCSP, 8-pin SOP

Overall EE Herald product rating: *** ( excellent)

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