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From multiple sensors to three sensor clusters in mobile phones: What does the future hold?

The growth of sensor use in mobile phones started more than 10 years ago. Image sensors first supplemented the basic microphones, followed by inertial, pressure and gas sensors. More are now coming, with existing sensors multiplying, so that there will be up to four microphones as well as 6-axis inertial measurement units (IMUs) paired with accelerometers.  New devices are also appearing, including ambient light sensors, depth sensors and infrared imaging.

Integrating such a diversity of sensors is becoming highly challenging, in terms of footprint, power consumption and processing power. So we, at Yole Développement (Yole) think that we are moving progressively towards integrating the existing and new sensors into predefined clusters. Actually, the three clusters already exist: the closed package sensor cluster, the open cavity cluster and the optical cluster. (See the latest report from Yole Développement, Camera Module Industry)

The closed package sensor cluster is simple and already well established. It includes inertial sensors, typically multiple axis accelerometer and gyroscope, and magnetic sensors. This cluster must be sealed in order to isolate the sensors from outside world, avoiding torsion and humidity, and is dedicated to motion sensing. In the future, it could also include other sensors but we think that most applications will use 6- or 9-axis IMUs plus potentially an accelerometer to provide a very-low-power always-on function. MemsIC and STMicroelectronics first introduced them into mobile phones in the early 2000s, making these clusters clearly the most mature and the most commonly integrated. Integration is done both on silicon, for gyros and accelerometers, and using a System-in-Package (SiP) approach for Application Specific Integrated Circuits (ASICs) and magnetometers. The trend is for more of both: more integration on silicon; and SiP integration for what is too costly to do on the same silicon.

Open cavity clusters will likely host the devices that need access to the external world. For example, pressure sensors can combine with humidity sensors and potentially gas sensors as all interface with the environment. There’s clearly an a big challenge to integrate them with inertial sensors due to potential crosstalk between the sensors, because torsion and humidity are not welcome in the motion sensing environment. But microphones are already well implemented in the mobile phone structure and need similar external access. So, we think that one of the microphones will host the environmental sensing of pressure, humidity and gas. It will lead to a very important combo, able to understand our surrounding environment, while the inertial cluster fine-tunes our location. Here the integration will be mainly SiP, as today most of the sensors are made using very different processes and are too costly to integrate on the same piece of silicon. However, you never know what innovation can bring. New technologies such as VesperMems’ thin-film piezoelectric microphone, which could be modified into a pressure sensor with few changes, demonstrates the potential opportunities.

We are also convinced that the third cluster will be optical. Image sensors are the most expensive sensor modules in mobile phones and are becoming a key selling point. Currently the annually upgraded camera module “just” takes pictures, but there is much greater potential for optical sensing. Many wavelengths are underexploited and can give access to face and iris recognition, 3D mapping, distance measurement, infrared and multispectral imaging. All are in the future and require new hardware development. But the increasingly dual optical cluster, encompassing front and rear image sensors, will also host existing optical sensors, like proximity sensors, ambient light and depth sensing. Integrated optical clusters will need optimization of silicon architecture, including defining the photodiode appropriately for the application, but mostly use SiP to bring together IC, image sensing, dedicated optics, auto-focus and stabilization. This optical cluster will be more of an optical module, with heterogeneous integration. The optical cluster/module is just emerging, meaning that the transition from image capture to sensing is on the way. We believe it will be much faster than expected (see the latest report from Yole Développement, Camera Module Industry Report).

What will happen to other sensors, such as fingerprint scanners? We think that they will integrate into other parts of the mobile phone. For example, fingerprint identification will happen in the touch screen, or a different sensor will identify the phone owner, for example the optical cluster for face or iris recognition. Otherwise, if you consider each sensor in turn they all could fit in one of the three sensor clusters we have defined.

When will integration into these three clusters happen? The closed sensor cluster already exists. The optical cluster is imminent because of major changes in the camera module that are happening now. Their evolution may take two to three years, where use cases are not yet clearly defined. Use cases of the environmental sensors in the open cluster are also not yet clear, so more marketing analysis is needed.

It is important to keep the recent appearance of the closed cluster in mind. The value of inertial devices has shifted dramatically from single devices to combos, but the prices of 3-axis or even 6-axis combos are falling very low. Now, value comes from the ability to provide a function – including having software enabling that function. Most device makers do not have this. Companies that will be affected by the emergence of the two other clusters need to be clear on what they are selling: is it devices or functions? The ability to generate long-term profit is at stake

Yole is launching a dedicated analysis on the development status and market for these three clusters. For more information about this ongoing analysis, please contact Jean-Christophe Eloy at eloy@yole.fr 

 

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Source:   Yole Développement

  

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