STMicroelectronics introduces high-performance MEMS-based rotational accelerometer for disk drive and consumer applications.

Business & High-Tech Editors

GENEVA--(BUSINESS WIRE)--Aug. 20, 2001

SO24-packaged device combines MEMS sensor plus interface chip,

providing 800Hz bandwidth and 2.5rad/s2 sensitivity.

STMicroelectronics (NYSE: STM) today introduced a new rotational acceleration sensor device based on Micro-Electro-Mechanical System (MEMS) technology that addresses applications in hard disk drives and consumer products.

Housed in an inexpensive standard SO-24 plastic package, the new L6671 device includes a capacitive rotational accelerometer sensor produced using MEMS technology plus a sensitive interface chip integrating the analog-to-digital conversion, filtering and interface functions. The L6671 provides a digital output through a 3.3V (5V tolerant) three-wire serial bus and achieves a signal bandwidth of 800Hz, sensitivity of 2.5rad/s2, a full-scale sensitivity of 200rad/s2 and a signal-to-noise ratio of 37dB over 30-800Hz. Through the serial bus it is also possible to program device characteristics including gain, offset, filter performance and phase delay.

Inside the device, movement about the rotational axis - the axis orthogonal to the package - causes a displacement of a structure inside the MEMS sensor thus producing a capacitive change. These changes in capacitance are converted by the interface chip into a digital output for direct connection to a microprocessor. The device can measure capacitance changes as small as 0.05fF (0.05x10-15F).

Sensitivity of the system is enhanced by the design of the interface chip, fabricated by ST in BiCMOS technology. It is also enhanced by the use of ST's in-house developed MEMS technology that has a deep layer of polysilicon used to make the moving parts of the sensor. This additional thickness translates into greater capacitance changes for a given acceleration. The ST MEMS process also includes an innovative technique for etching the sacrificial silicon dioxide layer beneath the moving parts, minimizing stiction effects.

In hard disk drive applications, the L6671 sensor device allows drive designers to reduce the effects of mechanical vibration on head tracking and thus increase the number of tracks per inch and hence drive capacity. In a typical hard disk drive, rotational vibrations act on the mass of the voice coil actuator used for head positioning, causing errors in the read/write head position. With the L6671 it is possible to detect and measure rotational vibrations so that the firmware can generate a feedforward correction signal for the voice coil drive circuit to keep the head in the correct position. This approach means that the track-to-track distance can be reduced significantly, increasing the density per unit area. In addition, the speed performance of the drive is enhanced because less time is wasted restoring the correct head position when vibration has caused the tracking to be temporarily lost.

Compared to solutions based on pairs of linear accelerometers the ST solution is much simpler, easier to use and more reliable as it is a single package and needs a minimum of external components. In addition, it connects directly to a microprocessor or system-on-chip through a serial digital interface. Physical position in the drive is non-critical because the sensor measures only the pure rotational component of vibration regardless of the origin. Moreover, the complete system is housed in a single, conventionally styled package compatible with standard production equipment.

STMicroelectronics is one of the leading producers of semiconductor devices for the hard disk drive and offers a complete range of products covering all of the functions of the drive. The company is also able to provide to customers a complete solution including all of the firmware in addition to the hardware components.

About STMicroelectronics

STMicroelectronics is the world's third largest independent semiconductor company. The Company shares are traded on the New York Stock Exchange, on Euronext Paris and on the Milan Stock Exchange. The Company designs, develops, manufactures and markets a broad range of semiconductor integrated circuits (ICs) and discrete devices used in a wide variety of microelectronic applications, including telecommunications systems, computer systems, consumer products, automotive products and industrial automation and control systems. In 2000, the Company's net revenues were $7,813.2 million and net earnings were $1,452.1 million. Further information on ST can be found at www.st.com.