MEMS Gyroscope Technology
MEMS (Micro-Electro-Mechanical Systems) technology is a vital enabling technology that has been invigorating and catapulting the growth of the sensor industry for well over a decade. MEMS IC fabrication processes and techniques allow for creating lower-cost, smaller devices with improved performance, on-board signal conditioning electronics and ease of integration into embedded consumer products. InvenSense is spearheading the creation of next-generation technologies to capitalize on existing and emerging market opportunities. Its current technology platform, called Nasiri-Fabrication, takes advantage of major innovations in MEMS mechanical design and fabrication, mixed-signal ASIC design and wafer-level packaging. Advances in these areas have resulted in the world’s smallest dual-axis rate gyroscope.
Various sensing technologies are used in gyro sensors, including piezoelectric, ring laser, fiber-optic, spinning mass, and capacitance. MEMS gyros, which can allow for reduced size and cost, are typically vibratory devices that use vibrating mechanical elements (a proof mass) to sense rate of rotation. Vibratory gyros are based on the transfer of energy between the two vibration modes of a structure, due to Coriolis acceleration (which arises in a rotating reference frame and is proportional to the rate of rotation). Tuning fork gyros contain a pair of masses that are driven to oscillate with equal magnitude, but in opposite directions. When rotated, the Coriolis force creates an orthogonal vibration that can be sensed using various sensing techniques.
One of InvenSense’s major technological advantages is its patented, out-of-plane, resonating structure. This structure is the cornerstone of a vibrating, dual-mass, tuning fork gyroscope design that outstrips the competition in its ability to serve the low-cost gyroscope market. Another key design advantage is wafer-level packaging for a fully functional device at the silicon die level. This is done by combining the MEMS and ASIC wafers using a proprietary and patented wafer- bonding technology that is unique to Nasiri-Fabrication.
Unlike typical resonating rate sensors, InvenSense’s gyroscopes do not require expensive hermetic packaging to achieve the required operating pressure or isolation from moisture and other environmental factors. Integrating all the signal conditioning electronics at the wafer-level with the MEMS is inherently superior in performance because of the minimization of stray capacitance and inductance.
Additionally, this level of integration minimizes the need for external components in the application, providing a major cost and size advantage. The wafer-bonding process provides electrical connections between the CMOS and MEMS wafers which also create a hermetic seal between the two wafers. Integrating the finished MEMS structures with a standard off-the-shelf CMOS avoids many of the pitfalls associated with trying to integrate the MEMS and CMOS processes, as with other MEMS gyro devices, requiring chip stacking of the MEMS with the ASIC or using the multi-chip packaging approaches all requiring more costly and nonstandard packaging and manufacturing.
About Nasiri Fabrication
Nasiri-Fabrication, protected by numerous patents, leverages innovative MEMS fabrication technology, proven bulk silicon micromachining processes, and low-cost, wafer-level packaging and integration techniques to achieve a very low-cost, single-chip sensing solution.
Nasiri-Fabrication supports a wide range of MEMS devices including gyroscopes, accelerometers, rotation sensors, actuators, and potentially many other MEMS devices. This process is particularly suitable for MEMS capacitive sensing types or devices requiring actuators. Unlike many MEMS inertial sensor manufacturers that must go through interconnects and wire bond to a companion chip, Nasiri-Fabrication process combines the MEMS to the CMOS allowing for direct electrical interconnection between the MEMS and its appropriate circuits. Though the process uses off-the-shelf wafer bonding equipment, the bonding technology itself is patented and proprietary, allowing for a eutectic bonding of the MEMS wafers directly to the aluminum layer on the CMOS wafer without the addition of any other layers on the aluminum. Nasiri-Fabrication reduces wafer-scale integration and packaging to a single step in the process by making electrical interconnects between the MEMS and CMOS. The process streamlines wafer-scale packaging by providing fully hermetic sealing of the sensitive MEMS structures.
Nasiri-Fabrication process has been ported to multiple high volume MEMS foundries, and is capable of producing thousands of gyro sensors with compensating electronics and wafer-scale packaging, on a single silicon wafer.
Gyroscope Applications
Smaller, low-power, less expensive MEMS gyros have key potential for use in consumer electronics applications. For example, in camera image stabilization applications, small form factor gyros can help ensure high-quality pictures by detecting and controlling hand jitter. As digital still cameras increase in pixel density and optical zoom range, subtle hand movements can result in poor image quality, especially in low-light settings. InvenSense’s integrated small form factor dual-axis gyros are enabling MEMS gyros to replace piezoceramic gyro sensors, which have been used in camcorder or camera image stabilization and which reportedly could be fragile and vulnerable to temperature drift.
Moreover, camera phone images tend to be of low resolution and are susceptible to blurring as a result of hand jitter. Cameras with higher resolution and optical zoom and auto focus capabilities will be vulnerable to blurred images. The small size of camera phones and their densely packed electronic circuitry has tended to prohibit the integration of the existing image stabilization solutions that are used in digital still cameras. InvenSense’s gyros can possess the size, power, and cost characteristics that meet the needs of camera phone manufacturers.
In handheld devices, such as mobile phones, InvenSense’s integrated dual-axis gyros can allow for more intuitive, gesture-based functionality, such as scrolling, text entry, improved GPS navigation, or gaming. The company’s gyros serve as “smart user interfaces” that provide mobile systems with a higher degree of motion and gesture comprehension, enabling them to provide enhanced intelligence and user interaction, and an improved user experience.
The company’s compact, cost-effective gyros could also, for example, facilitate using handheld electronic devices for pedestrian navigation or location-based services. Such services can include emergency assistance, pedestrian navigation/tracking, and mobile commerce (e.g., using a mobile phone to search for a restaurant or other points of interest). Such pedestrian navigation and location-based services require a global positioning system or terrestrial tracking technology. Moreover, in such applications gyros can provide information about direction of motion, which, along with information from accelerometers, can aid in pinpointing the user’s location and in accurately tracking the user’s position and movements when a GPS signal is compromised or unavailable.
InvenSense’s product road map includes a six-axis Motion Processing Unit™ (MPU™), sensing all six degrees of freedom using its gyroscope and accelerometer technology, providing for more intuitive and comprehensive motion sensing capabilities. The six-axis MPU will provide dynamic motion to benefit applications in mobile phones or other consumer electronic handheld devices. Such applications could include location-based services (where the MPU would provide dead reckoning for better position tracking), image stabilization, user interface control, gaming, and power management.
BlurFree & StrayFree
In addition to producing motion sensors, InvenSense develops complete application solutions to enhance product functionality while expediting adoption and time to market for product manufacturers. It’s BlurFree™ image stabilization technology uses the gyroscope with specially designed imaging algorithms which provides superior image quality for digital cameras and camera phones. The gyroscope accurately tracks the movement of the camera caused by the natural hand shake of the user and the BlurFree™ software corrects the blur caused by this motion. The results are sharper pictures that are typical of more expensive mechanical image stabilization systems. For GPS applications, InvenSense’s StrayFree™ dead reckoning technology provides an autonomous and highly accurate navigation solution when a GPS signal is corrupted or unavailable for handheld and portable navigation devices (PNDs).
Image Stabilization Technology
As Digital Still Cameras (DSC) become smaller, cheaper and higher in resolution, photographs are increasingly prone to blurring from natural hand shake. Image stabilization is an effective solution that addresses the quality of images and is quickly becoming a standard feature that consumers are asking for in today’s cameras.
DSC makers today reduce blur using software techniques that include a high ISO and motion vector calculations. The drawback of such methods is increased system memory and significant processing requirements. In addition ISO reduces the exposure time resulting in undesirable artifacts such as pixel noise affecting overall image quality. These drawbacks result in software solutions providing limited performance. Mechanical stabilization uses the gyroscope data to accurately track the hand jitter and compensate in real time by moving either the lens or the sensor optics module. While providing great performance, this type of solution is expensive and requires significant optics expertise
InvenSense’s BlurFree™ technology provides superior image quality for cameras and video systems by using a gyroscope to accurately track the movement of the camera caused by the natural hand shake of the user. The results are sharper pictures that are typical of more expensive mechanical image stabilization systems. The BlurFree™ technology running on the image processor converts in real time the hand shake information from the gyro into a digital format known as Point Spread Function (PSF). Image data is then processed in real time and the best picture with the least amount of blur is selected
POINT SPREAD FUNCTION
The pictures below show the movement of the camera due to natural hand shake. The PSF is captured using InvenSense’s IDG-1000 gyro and a 10 MP digital camera.
: used with InvenSense’s motion sensors provides an autonomous and highly accurate navigation solution in handheld and portable navigation devices (PNDs) without interruption when a GPS signal is corrupted or not available.
MPU™: Motion Processing Unit, InvenSense trade mark
iG™: Instant Gesture, InvenSense trade mark