MEMS integration: A Matter of Perspective
May 24, 2012
Latest foundry results underscore the change in MEMS ecosystem
July 27, 2012Easier integration through standards
In a previous post, I discussed the challenges of MEMS integration and primarily looked at design methodology improvements that could help address the issues engineers face. But there is also the issue of how to standardize the process of designing – and more importantly, integrating – the various elements of a MEMS-based system.
Most industry observers suggest that the way forward is through standardization of hardware and software interfaces. On the hardware side, the system companies would like to see standardization at the digital interface level, such as compatibility with I2C bus. To address this requirement, MEMS-based sensors are such as microphones, accelerometers and gyroscopes are increasingly being labeled as digital, meaning they have a digital rather than an analog hardware interface. Thus, a MEMS component may actually be a sub-system that combines a microcontroller, an A/MS ASIC, and the MEMS sensing element in a single package. A 10 degree-of-freedom motion sensor component, for example, includes a 3-axis accelerometer, 3-axis gyro (usually 2 or 3 separate MEMS), a 3-axis magnetometer (compass), and a barometric pressure sensor, all packaged together with A/MS circuits and a microcontroller. But there are opportunities for standardization of higher-level software layers as well. For instance, combining the output from 10 sensors into the position and orientation information that’s needed by application developers is a nontrivial task that is now handled by “sensor fusion” software. Leading vendors of motion sensors such as ST Microelectronics and Invensense, as well as a number of software startups, are providing sensor fusion software to make it easier for application developers to utilize input from motion sensors.
The standardization of software and hardware interfaces to MEMS components will surely happen, either as a result of industry standardization efforts or de facto standards imposed by a dominant component supplier. At the physical level, perhaps interfacing with I2C bus will become mandatory for market success. At the application level, the programming interfaces to sensor fusion software will no doubt converge. The crucial question, for both system integrators and MEMS component suppliers, is “When?” The standardization and/or convergence of interfaces will undoubtedly take a number of years. In the interim, both MEMS component suppliers and system integrators will continue to face substantial integration costs, both in engineering effort and time to market.
Abstraction shields complexity
As usually occurs when systems get more complex, higher-level layers of MEMS-enabled systems are being shielded from lower levels by interfaces that abstract details of the lower layers. The emerging stack of software and hardware layers for sensor-enabled smart phones is illustrated in Fig. 1. At the highest level are sensor-enabled apps such as augmented reality apps that use knowledge of the phone’s position and orientation to annotate the camera output with useful information. The augmented reality app in turn makes use of the sensor fusion software, which runs as a service provided by the phone’s operating system. The operating system requires generic or vendor-specific software drivers to interface with the sensor components via a hardware bus such as I2C. And the sensor components include their own stack, from firmware, to microcontroller to A/MS circuitry and finally the MEMS sensing elements themselves.
We are in a transitional period in which the dominant MEMS suppliers are racing to provide vertical integration across the stack. For instance, a MEMS supplier that also supplies sensor fusion software (with a proprietary interface) hopes to gain competitive advantage by locking in apps developers. Once an app is developed to one vendor’s motion interface, porting to another vendor’s interface may require a considerable effort. Meanwhile, system integrators, app developers and operating system vendors would prefer a sensor fusion layer that’s independent of the underlying sensing components, allowing them more choices of MEMS component suppliers. Recognizing this need, startups such as Movea and Sensor Platforms offer sensor fusion interfaces that are hardware independent. Under the covers, these startups have to do the integration with different hardware, and that’s part of their value add. The competition between vertically integrated suppliers and new entrants who offer value by isolating systems integrators from vendor-specific interfaces will continue at all levels of the sensor stack. Over time, the market momentum could shift from vertically integrated MEMS suppliers to companies that specialize in horizontal layers, as it has in other, more mature sectors of the technology industry.
![Fig. 2. Silicon spin qubit centered in the dotted circle, control and readout signals (M, P, R, T, and Q) are shown in the inset. Simplified schematics of the quantum point contact and corollary circuits are shown. The voltage source is implemented as a digital-to-analog converter at room temperature. (Taken from [6])](https://www.coventor.com/wp-content/uploads/2022/05/Fig.-2.-Silicon-spin-qubit-centered-in-the-dotted-circle-control-and-readout.png)
![Figure 2: Schematic view of standard CMOS including an electro-mechanical switch monolithically integrated into BEOL [2]. Courtesy: University of California, Berkeley](https://www.coventor.com/wp-content/uploads/2022/04/Figure-2-April-2022-MEMS-Blog-for-Coventor-website.png)
