MEMS pressure sensors solve new pain points in human-machine interface

In May 2021, Qorvo announced the acquisition of NextInput. As the first acquisition of its sensor fusion product line, Qorvo has high hopes for NextInput's innovation in improving the human-machine interaction (HMI) market. At the same time, it also means that in addition to RF MEMS, Qorvo also has the technical accumulation of MEMS pressure sensors.

Ali Foughi, founder and CEO of NextInput, said at the time of the acquisition: "We will continue our mission to bring innovation and revolutionize the touch experience through outstanding sensing solutions. Qorvo's broad portfolio of complementary technology products and world-class supply chain capabilities enable us to expand our business quickly. After joining a global leader in semiconductor solutions, we hope to continue to create success in the HMI (human-machine interface) market."

So, one year later, what has Qorvo done in terms of pressure sensors? We recently interviewed Qorvo engineer Will Wang and asked him to introduce the current status and prospects of pressure sensors in the HMI field, covering mobile phones, wearables, and automobiles.

How big is the imagination space for pressure sensing?

Will said that MEMS pressure sensors are a new interactive supplement to traditional touch. Intuitively speaking, "touch" is an action, and "pressure" is also an action. When your finger clicks on an APP on the phone screen, the brain will get the expectation of "opening". At the same time, when you press an object, the brain will expect different results depending on the different strength of the pressing surface. This is what the pressure sensor is supposed to achieve - accurately determine the force applied to the object and enable the device to complete the brain's expectations.

Compared with the two-dimensional capacitive sensing solution with only XY axis, combining pressure sensor with capacitive sensor can increase the data interaction of Z axis (vertical direction), thus bringing more possibilities for HMI applications. In addition, because the data volume of Z axis pressure is richer, it is not only possible to realize a simple on/off operation, but also to transmit more information through different pressure values.

At the same time, another way is to deploy multiple pressure sensors and cooperate with corresponding algorithms to achieve XYZ three-dimensional recognition only with pressure sensors. This technology can theoretically adapt to a variety of environmental challenges including metal, thick gloves, and water operations.

Theoretically, in any scenario where mechanical buttons or capacitive touch switches are used, you can try to use pressure sensors as replacements, which has many advantages such as no need for punching, no accidental touches, and enhanced waterproofness.

However, Qorvo’s ambition in HMI is not just to be a “button replacement”, but has a broader scope for imagination.

A variety of pressure sensor technologies to meet different applications

Pressure sensitivity enhances the operating experience of gaming phones

If pressure sensors want to replace capacitors or other sensors, the most important thing is to find the application pain points. Pressure sensors first appeared on iPhone 6s and implemented the 3D Touch function (Peek and Pop), but this function lacked enough killer usage scenarios, so it did not gain widespread favor from users and developers. A few years later, Apple decisively replaced 3D Touch with Haptic Touch, using software to implement similar functions, thereby saving costs and power consumption. The same is true for the Android ecosystem.

However, with the segmentation of the mobile phone market, including the emergence of new formats such as gaming phones and folding screens, Qorvo has seen new opportunities and successfully introduced them into products including Black Shark, Meizu, iQoo, etc. For example, in Black Shark, by combining pressure sensors and Black Shark's dedicated setting software, dual-zone screen pressure-sensitive touch operation is realized, adding more differentiation to the game. For example, in MOBA games, the pressure-sensitive function can instantly add blood and change clothes when moving and attacking. In FPS games, you can press and shoot when aiming and press and lie down instantly when walking and shooting, etc. In racing games, you can flexibly control the throttle and brake force in the full screen range. A series of examples show that pressure sensors facilitate operation and enhance the game's combat experience. In addition to games, pressure sensors have also been expanded by Black Shark to pressure-sensitive navigation in system applications. Users can press the screen anywhere to drop out the operation navigation, making the phone a one-handed operation artifact.

Will added: "Pressure sensing can achieve more accurate operations without being triggered by mistake. This demand will grow with the emergence of full-screen, foldable screens, gaming phones, etc."

According to reports, there are currently two solutions for implementing pressure sensing. One is in the form of a module, using an MCU to process pressure sensing signals. This module is composed of multiple FPCs, so multiple large holes must be opened in the phone's middle frame, and the durability and yield of the FPCs have some drawbacks.

Qorvo's solution is to use a single chip that integrates sensors and analog front-ends, which can communicate directly with the CPU without the need for an MCU. It has smaller openings, has relatively less impact on ruggedness, heat dissipation, etc., and is easier to install.

According to Will, Qorvo's current solution only requires two chips to achieve dual-finger pressure detection on the upper and lower screens.

For pressure sensor applications without side buttons, Qorvo will provide sensor fusion solutions, including pressure sensors, infrared sensors, ultrasonic sensors and single-chip solutions implemented with analog front-ends. IR plays a positioning role, so that pressure sensing can be easily achieved with only one sensor, thereby simplifying the design and avoiding accidental touches.

Importantly, Qorvo can provide complete hardware solutions and software algorithms to remove design barriers and allow customers to focus more on differentiating their applications using pressure sensors.

TWS fully reflects the difference in pressure sensitivity

Although Apple did not choose pressure sensors in later iPhones, it fully embraced pressure sensors in TWS. The main pain point of HMI for TWS applications is false touches of capacitive sensors, including hair, rain, sweat, grease, etc., which can cause false touches and affect the experience. In addition, for those who use MEMS acceleration sensors to operate by tapping, the actual experience is not as direct as pressure sensors. It is understood that the pressure sensors currently used in TWS have been gradually introduced from the mid-to-high-end market to the mid-end market.

Will said that for TWS applications, Qorvo's products are more suitable for this scenario due to their single chip, small size, support for digital output, simple modules, etc. And as more cases are introduced in the market, customers are becoming more and more confident.

Other wearable devices

In addition to TWS, pressure sensors also have broad development prospects in watches, bracelets and even AR/VR devices. Taking smart watches as an example, Google-Fitbit adopted Qorvo's solution to replace the mechanical switches, knobs or sliders in the watch, making the watch more waterproof.

However, Will also mentioned that there are still many debates about whether to cancel mechanical buttons for smart watches, such as the aesthetic perception of watches or functions such as heart rate measurement, which cannot replace mechanical buttons. But at least for the capacitive touch solution in wearable devices, pressure sensors are fully capable and support underwater/humid environments, making it possible to have a better experience.

Improved experience of productivity tools

Pressure sensors are also very suitable for productivity tools. Taking Apple as an example, its notebooks have always adopted Force Touch technology and have been widely recognized by customers. Now this technology is being favored by more brands.

In addition, for tablets and handwriting tablets used in productivity, pressure sensors can simulate functions such as "paintbrushes" by virtue of their high-order and delicate Z-axis response.

Automobiles will be another flashpoint

Qorvo also expressed its attention to the automotive market. As the only pressure sensor supplier that has passed automotive-grade certification, its products have been widely used in models including Tesla, Geely, and Chery, and have passed PPAP certification from three Tier 1 suppliers including Valeo, Yanfeng, and Joyson.

Its application scenarios include car doors, multi-function steering wheels, central control, etc., among which Tesla alone uses more than 10 pressure sensors. Especially with the deepening of the concept of "putting wheels on mobile phones", we can see that the interior of the car's cab, whether it is the dashboard, the main control screen, the central control panel or even the co-pilot screen, is moving towards more and larger directions, and mechanical buttons and knobs are gradually being replaced by virtual buttons on the LCD screen. Under this change, the car cockpit has changed from being surrounded by mechanical buttons, knobs and indicator lights like the cockpit of an airplane in the last century to being presented in a more friendly, flexible and simpler way with screens everywhere. This has brought demands for automotive HMI far beyond the mobile phone market, and also given pressure sensors more room to display.

High quality is the basis of experience

Last but not least, product reliability is the foundation of all user experience. Not to mention being unable to accurately command a car on a fast highway, even when playing games, an unnecessary touch error will make players feel frustrated.