MEMS Accelerometer Sets Size And Cost Benchmarks

Jan. 24, 2012
The MEMSIC MXC626Xc accelerometer is based on a thermal technique that enables higher reliability in the industry’s smallest package for the lowest cost, according to the company.

Fig 1. Wafer-level BGA packaging and a patented heated-gas thermal acceleration measurement method combine to produce MEMSIC’s MXC626Xc two-axis digital accelerometer, which is small enough to be threaded into the eye of a sewing needle. It also lends itself to higher integration levels, making it the lowest-cost accelerometer on the market.

Fig 2. The single-chip MXC626Xc integrates all of the necessary signal conditioning and other circuitry.

Thanks to its patented thermal heated-gas principle of measuring acceleration and the use of novel ball-grid-array (BGA) and wafer-level packaging (WLP), the MEMSIC MXC626Xc breaks records in size and cost. The two-axis, ±2-g (X/Y) accelerometer produces an 8-bit digital output in a tiny package that measures 1.2 by 1.7 by 1.0 mm at a single-unit OEM price of just 35 cents ($0.35).

The MXC626Xc not only is the smallest and lowest-cost accelerometer in production, according to the company, it’s small enough to literally fit within the eye of a sewing needle (Fig. 1). Despite its size, which is approximately 50% smaller than competitive offerings, it can handle a shock of 50,000 g, which is about five times greater than the shock survivability of typical capacitive-type accelerometers.

Manufactured on a standard CMOS 0.18-µm process, the package integrates all of the necessary signal-conditioning, programming, and processing circuitry including a clock generator and sequencer, a reference voltage and bias-current generator, a control and data register, a PC interface, and a DSP. There’s also a two-axis sensor, an amplifier, an analog-to-digital converter (ADC), and sensitivity, thermal-compensation, and fine-gain adjustment circuitry (Fig. 2).

The MXC626Xc’s small size and low cost suit it well for a number of consumer electronics applications such as mobile phones, digital still cameras, digital video cameras, toys, and MP3/4 players. It is also aimed at home appliances and items like clothes irons, halogen lamps, fan heaters, and cooling fans.

The accelerometer detects four-position and shake-detection orientation. Its two-axis acceleration features a very low 0-g offset with a typical temperature coefficient of 0.6 mg/°C. An I2C interface is included for communications with the device, as is an interrupt pin for shake and orientation.

The chip operates from a supply of 2.5 to 5.5 V and draws 1 mA of current in the power-up mode. A power-down mode, enabled via the I2C interface, allows a mere 1 µA of maximum current drain. Turn-on time is typically 300 ms, and the operating-temperature range is –20°C to 70°C. 

Other typical parameters for the X/Y axis include ±1.0º alignment error, ±5.0% sensitivity error, 64 LSB/g sensitivity, ±15 % sensitivity drift over temperature, and ±50 mg of zero and offset bias level. Its 3-dB bandwidth is 10 Hz.

No Moving Parts

Since the MXC626Xc uses the heated-gas approach for measuring acceleration, it has no moving parts. It uses resistive heating to heat the gas molecules and thermocouples or other temperature sensors to measure the temperature difference between the two sides of the heater when there is no acceleration and when acceleration is applied.

The MXC626Xc is inherently more reliable than capacitance-type accelerometers. It is also amenable to monolithic manufacturing, resulting in lower-cost and higher-reliability solutions Capacitance-type microelectromechanical-systems (MEMS) accelerometers, meanwhile, use a solid mass structure that measures the capacitance difference between two sets of inter-digitated plates and is prone to stiction.

The MXC626Xc is available for delivery within eight weeks. Samples are available upon request.

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