A solid-state haptic button is a fixed, non-moving control that combines force sensing with localized haptic feedback to replicate the feel of a mechanical switch. Because nothing physically travels, designers can build seamless, sealed device edges while gaining a programmable input surface — one whose stiffness, click feel, and behavior are defined in software rather than by a spring and dome.
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Key Takeaways
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What is a solid-state haptic button?
A solid-state haptic button is an electromechanical interface that pairs a force or touch sensor with a haptic actuator, typically a piezoelectric element, so that pressing a rigid surface produces the tactile sensation of a physical click. Smartphone OEMs have explored the concept since the iPhone 7 home button (Apple, 2016) and the HTC U12+ pressure-sensitive frame (2018), both built on linear resonant actuators. Boréas Technologies demonstrated a piezo-based implementation with its SmartClik platform in 2019, using TDK PowerHap actuators driven by CapDrive® piezo driver ICs.
Force sensing and haptics open an interactive dimension designers can use to build a better user experience and a stronger emotional bond between product and user. The framework below describes how OEMs can approach a solid-state interactive design initiative, layer by layer.
Common approaches and their limits
Every button technology trades feel, design freedom, and cost differently. The core question for a solid-state design is whether the actuator can produce a click sharp and localized enough that users cannot tell the difference from a mechanical switch.
| Approach | How it works | Main limitation | Typical use case |
|---|---|---|---|
| Mechanical switches | A spring or dome collapses under force, giving a physical click and closing a contact. | Moving parts wear out, require chassis cutouts, and complicate sealing against water and dust. | Volume and power buttons on most phones and wearables today. |
| LRA-based solid-state buttons | A linear resonant actuator vibrates the whole device body when a press is detected. | Vibration is global and resonance-limited. The click feels diffuse, soft, and noticeably artificial. | Early attempts: iPhone 7 home button, HTC U12+, Vivo concept phones. |
| Piezo solid-state buttons (Boréas approach) | A piezo actuator under the button zone delivers a sharp, localized click, driven by a high-voltage IC that also senses press force. | Requires a high-voltage driver IC and mechanical integration of the actuator stack. Higher BOM cost than a simple dome switch. | Sealed smartphone edges, AI glasses, smart rings, automotive controls. |
The three interactive design layers
1. System design layer
The system design layer is the foundation of a successful solid-state haptic button integration. It covers all the functional requirements that make the experience transparent to the user. The goal is a tactile experience where the user cannot notice the difference between a mechanical switch and a haptic button in force, feel, and latency.
Phone OEMs that used LRAs for solid-state buttons fell short at this layer. LRAs are fine for device-wide haptics but lack the sharpness and stiffness of a mechanical click. Piezo haptic feedback is localized and sharp, and integrated force sensing lets designers tune the button's apparent stiffness in software.
Risk if not well implemented: this layer is non-negotiable. A solid-state button that doesn't feel right fails at the first press. Poor feel is what generated negative reviews for early LRA-based devices.
Risks if not well implemented:
The system design layer is the foundation for solid-state haptic buttons to meet the basic end-customer requirements and mass market adoption. OEMs can't ignore or bypass this layer. Solid-state buttons that don't feel good feel unnatural to the user. Using LRAs in solid-state buttons will inevitably result in poor performance and negative product reviews. A solid tactile foundation is critical to make the transition to solid-state buttons as seamless as possible.
Contextual Design Layer
The sense of touch is excellent for conveying contextual information between the device and the user. In addition, well-executed haptic feedback is a simple way to share critical information in an intuitive, non-obtrusive way while keeping the user's cognitive load to a minimum.
The contextual design layer is where the OEM starts customizing the solid-state haptic button behavior to share contextual information with the user. Force sensing and custom haptics enable a new dimension of interaction through the entire OS. Therefore, the first goal is to leverage force sensing to improve navigation. The second goal is to leverage custom haptics to enhance usability. The user should know the device's current contextual state, what to do and what to expect through touch.
Examples of contextual force sensing navigation improvements:
Different force levels that unlock submenus
- A strong power button press opens the shutdown menu (shut down, restart, and emergency call)
Example of custom contextual haptic feedback
- Normal volume up/down haptic feedback: Normal system click
- Volume Max and Min haptic feedback: Bounce. It's the end of the spectrum. The user knows that pushing again won't do anything.
Risks if not well implemented:
The user notices the contextual design layer. Therefore, building intuitive, functional, seamless navigation and haptic feedback is essential. Furthermore, the features should be distinct and easy to learn and remember for the user. Otherwise, there is a risk the user will believe the contextual layer to be confusing and annoying.
The Immersive Design Layer
Touch is the most intimate human sense. Leveraging haptics to craft enjoyable and unique experiences is a simple way to create a deeper emotional bond between the device and the user.
The immersive design layer lets designers be creative with solid-state haptic buttons. The goal is to leverage haptics and force sensing to create enjoyable and memorable touch experiences. Designers can customize the solid-state haptic button behavior to entirely change how it operates and feel and create an immersive experience.
Examples of force sensing immersive design:
DSLR camera shutter button "feel" using the volume button
The shutter button on a DSLR camera feels very different than a smartphone volume or power button. So let's see how we can leverage force sensing and haptics to replicate the DSLR shutter button feel and features on a smartphone.
Force Sensing
Smartphone buttons usually are pretty stiff. DLSR cameras, on the other hand, are very soft. They also have two levels: Mid-click triggers the autofocus, and full-click triggers the shutter.
Solid-State Button Customization:
Increase force sensitivity to reduce button stiffness. Detect two force levels. Map features for the two levels click. Mid-click triggers autofocus. A full click triggers the camera shutter.
Haptics Customization
Smartphone buttons are very sharp. The first DSLR button level (mid-click autofocus) is very soft, and the second click (full-click shutter) is sharper and stronger.
Solid-State Button Customization:
Mid-level click feedback = Rounded soft click
Full-Click = Sharp strong click
BOS1921 Settings Examples
We mapped the BOS1921 parameters we used to replicate two different DSLR cameras:
| Model | Button | Vmin (V) | Vmax (V) | Frequency (Hz) | Cycles | Button Press Threshold (mV) |
|---|---|---|---|---|---|---|
| Panasonic G7 | Shutter (1st level) | 0 | 60 | 100 | 2 | 150 |
| Panasonic G7 | Shutter (2nd level) | 0 | 60 | 150 | 1 | 250 |
| Sony a6400 | Shutter (1st level) | 0 | 50 | 100 | 2 | 150 |
| Sony a6400 | Shutter (2nd level) | 0 | 60 | 225 | 1 | 550 |
Risks if not well implemented:
Too much immersive design can get confusing for the end user. Designers must be careful with how much information they want to share via touch.
Piezo haptics is the key to solid-state haptic button adoption
The adoption of the linear resonant actuator in the last few years significantly improved the smartphone user experience. However, LRAs don't reach the required performance for effective solid-state haptic buttons. An LRA vibrates the entire device and isn't sharp enough to create a good illusion. As a result, your users will notice something is off, negatively impacting the user experience. You can look at early attempts with the iPhone 7 home button and HTC U12+ device.
The only solution that can achieve all three interactive design layers is piezo haptics with our proprietary CapDrive® Technology.
Piezo actuators outperform LRAs and legacy technologies with localized haptics, customizable waveforms and high acceleration.
CapDrive® is our proprietary architecture technology for piezo haptics. The BOS1921 piezo driver drives waveforms up to 190 Vpk-pk from a 3 to 5.5 V supply and integrates piezo sensing with 7 mV resolution, so the same IC detects the press and plays the haptic feedback. It comes in a 2.1 × 1.7 mm WLCSP package, and a dedicated SYNC pin synchronizes multiple BOS1921 ICs within 2 µs for multi-button designs.
Start Experimenting with the Piezo Solid-State Button Devkit
The best way to understand the value of piezo haptics is with one of our development kits. The Piezo Solid-State Button Devkit with Captouch is built around the BOS1921 and offers a plug-and-play experience: a pre-integrated button module, so you evaluate the technology itself instead of debugging a first integration. You can use our free Haptic Studio software to quickly adapt haptic feedback to your design initiative.
Order your Piezo Solid-State Button Devkit here.
Frequently asked questions
Can a solid-state haptic button feel like a mechanical button?
Yes, that is the entire goal of the system design layer. Piezo haptic feedback is localized, solid and sharp enough to match a mechanical button's force, feel, and latency, and integrated force sensing lets designers customize the button stiffness. LRA-based buttons cannot reach that sharpness.
Why did early solid-state buttons like the iPhone 7 home button feel off?
They used linear resonant actuators. An LRA vibrates the entire device and isn't sharp enough to create a good button illusion, so users notice something is off. The iPhone 7 home button and the HTC U12+ are the reference examples of this limitation.
What is the difference between an LRA and a piezo actuator for buttons?
An LRA vibrates the whole device, which works well for notifications but feels diffuse as a button click. A piezo actuator delivers localized haptics, customizable waveforms and high acceleration, which is what a convincing button replacement requires.
How much power does the piezo driver consume?
The BOS1921 consumes 350 mW while driving a 100 nF actuator at 190 Vpk-pk and 300 Hz, with energy recovery returning unused charge to the supply. In sleep mode, quiescent current drops to 0.5 µA with state retention.
Glossary
Solid-state button: A button with no moving parts that combines force sensing and haptic feedback to replicate a mechanical click.
LRA (linear resonant actuator): A vibration motor that oscillates a mass at its resonant frequency, vibrating the whole device.
Piezo actuator: A ceramic element that deforms when voltage is applied, producing fast, localized haptic feedback.
Force sensing: Measuring how hard a user presses a surface. On the BOS1921, the piezo element itself is the sensor, read with 7 mV resolution.
Related reading
BOS1921 piezo driver IC with advanced sensing: specifications
Solid-state piezo button application overview
Solid-state buttons for mobile phones
How CapDrive® technology reduces piezo driver power consumption
Boréas Haptic Studio waveform design software
Next steps
Start experimenting with the Piezo Solid-State Button Devkit with Captouch → https://www.boreas.ca/products/piezo-solid-state-button-devkit-with-captouch
Discuss your solid-state button design with our applications engineering team → info@boreas.ca
Request the BOS1921 datasheet and documentation → https://www.boreas.ca/pages/bos1921-kit-technical-documentation
About the author
Marc-André Morin, Marketing, Communication & Distribution Manager, Boréas Technologies.
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