Touchscreen OLED displays are expected to redefine automotive user interfaces

The size and number of in-car displays are one of the top considerations for new car buyers when judging the technology and innovation of a car. The size of the in-car display is becoming a new driver of purchasing decisions. Whether it is a fuel-powered car, an electric car, or a hybrid car, the size of the in-car display often affects people's perception of the car's performance.

Automakers know that first impressions are hard to change, so they are paying more and more attention to the design of human-machine interface (HMI) displays, constantly pursuing not only big, but also perfect. Organic light-emitting diode (OLED) display technology can not only leave the best first impression on consumers, but also give cockpit designers more room to play, and users can also personally experience the tangible benefits.

According to a recent report by the Korea Display Industry Association (KDIA), the global automotive display market is likely to grow at an average annual rate of 7.8%, from US$8.86 billion in 2022 to around US$12.63 billion in 2027[1]. The use of OLED displays in cars is considered one of the drivers of this growth. In 2022, OLED only accounted for 2.8% of the market share, but this proportion is expected to rise to 17.2% by 2027.

Let’s look at the factors driving the growth of automotive OLED display technology.

OLED technology in car displays

Until recently, liquid crystal display (LCD) technology has been the dominant technology for in-car displays. This mature and well-established display technology originated in the consumer industry and was later specifically adapted for automotive applications.

From smartphones to computer monitors and TVs, the modern consumer industry has begun to shift to OLED display technology because it combines high-quality visuals with a thin and light form factor, and the automotive industry has similar needs and some automotive reasons, so the automotive industry has also begun to adopt this technology. In fact, many inherent characteristics of OLED technology are very attractive for automotive display applications.

True black and high contrast

Since OLED is an emissive display technology, no light is emitted when the pixel is turned off, so the black presented is "true black". In contrast, LCD technology presents black by blocking the light from the backlight unit, so the final presentation is dark gray rather than "true black". LCD manufacturers have tried to overcome this shortcoming by using mini-LED arrays to achieve local dimming and turn off the backlight in black pixel areas. Although this approach can improve contrast, it lacks pixel granularity and may cause undesirable display effects such as haloing. In addition, the added layer of mini-LED array and its electronic control components increase the thickness, weight and cost of the system. These shortcomings will become even more serious as the screen size increases.

What benefits can OLED display technology bring to car users?

• Most in-car graphical user interfaces (GUIs) use a black background to avoid distracting drivers and passengers when driving at night. Thanks to the pure black characteristics of OLED, user comfort is greatly improved.

• High contrast improves display readability and helps improve the overall safety of the vehicle.

• Wide viewing angles ensure that the display can be clearly seen from different positions in the car.

• Unlike other display technologies, OLED displays can still respond quickly in low temperature environments. Even on a cold winter morning, OLED displays can clearly present key real-time information without delay, helping you start a beautiful day.

• OLED is easier on the eyes because there is no need to switch the backlight, which reduces fatigue from long-term viewing.

Integrated cockpit design and lower power consumption

OLED technology helps automakers solve multiple challenges. As display sizes increase, the advantages of OLED technology over LCD technology will become more apparent. With fewer layers and thinner structures, OLED can give auto OEMs more room to improve the quality of cockpit design, such as:

• The lighter and thinner stacking structure helps reduce the weight of larger screens.

• The curved display screen is designed with a smaller radius, which can help create innovative cockpit designs and highlight brand identity.

• Thanks to Pure Black technology, the edges of the display blend into the black frame, giving the HMI module a unique look.

• Low power consumption, especially when the background image is dark.

• Environmentally friendly, using less plastic than similar LCD products.

Low power consumption and thinner, larger displays are particularly beneficial to electric vehicle manufacturers because they can provide longer driving range with the same battery capacity.

OLED technology has been adapted to automotive requirements

Automakers and suppliers are well aware of the shortcomings of older OLED displays, such as burn-in caused by many static (often unused) icons in the in-car GUI and poor readability in sunlight due to low screen brightness, but these issues have been resolved as OLED technology has improved.

With dual-layer OLED technology or tandem OLED structures, display manufacturers have significantly improved display brightness. In addition to brighter screens, the added organic layer in the OLED structure also spreads energy across the OLED to improve stability and extend life. Tier 1 automakers have recognized these improvements and are increasingly adopting OLED displays in their premium vehicles.

Touch interface

Regardless of the display technology used, the touch interface is key to delivering a great user experience. And the requirements for touch screens in cars are much higher than those in consumer devices. These include:

• It can still operate reliably under a wider range of environmental changes.

• Supports operation with gloves.

• It has electromagnetic compatibility in terms of immunity and radio frequency emission.

• Achieve ASIL-B level of functional safety standard ISO26262, as safety-critical mechanical buttons are gradually replaced by virtual buttons on touch screens.

In recent years, most LCD display manufacturers have integrated multi-touch functionality into their display products using On-cell or In-cell technology. Since OLED technology uses a full low-impedance cathode layer above the pixel, it only uses an On-cell structure. Currently, all major OLED car manufacturers have or are developing this design because it can achieve thinner, lighter, and more flexible touch OLED displays.

Figure 1: Automotive On-cell Touch OLED Stacking Structure

Although the adoption of on-cell technology allows OLED displays to be thinner, it also brings new challenges to the touch screen controller. This is because the touch electrode becomes closer to the cathode layer and the display pixel (see Figure 1: Automotive on-cell touch OLED stack structure). With the on-cell design, the capacitive load of the touch electrode to ground is now higher. Although the finger touch capacitance size has not changed, the sensitivity of the finger touch has decreased.

Here is an example to illustrate this challenge: With the previous display technology, detecting the capacitance of a finger touch is like measuring the change in the water level after pouring a glass of water into a small bucket. With the thin On-cell OLED structure, detecting the capacitance of a finger touch is now equivalent to measuring the change in the water level in a bathtub full of water!

Touch Controller

The electromagnetic noise generated by pixel switching and its stronger coupling with the touch electrodes increase the risk of false or missed touch detection.

Therefore, when selecting touch screen controller technology, it is necessary to pay attention to the signal-to-noise ratio (SNR) detection capability. The touch screen controller must implement the following functions:

• Drive and detection solutions adapted to the high-load characteristics of On-cell OLED touch sensors.

• Powerful display noise reduction technology.

• Fast and efficient signal processing for increased touch reporting rates and reduced first touch latency.

The appearance is full of technology

OLEDs deliver premium visuals, true black backgrounds, improved energy efficiency, and lightweight curved panels, making end products appealing to modern buyers and driving positive purchasing decisions.

Despite the technical challenges of thin automotive On-cell OLED technology, the user's touch experience must be perfect. Microchip's maXTouch® touchscreen controllers not only have proven technology for fast, accurate and waterproof multi-touch detection (even with gloves), but also have wide flexibility to adapt to the screen aspect ratios used in automotive designs. The latest M1 generation maXTouch touchscreen controller introduces new drive and detection mechanisms, and with advanced signal processing technology, it ensures fast, reliable and safe touch operation on the new automotive OLED display.

References