When you walk into a cinema and face a screen over ten meters wide, few people stop to think: why is it that when the screen is blown up so large, you can barely see any trace of a pixelated "mosaic"?

If you keep enlarging a photo on your phone, you will eventually see the pixels that make up the image. If you look closely at a computer monitor, you can also see the red, green, and blue sub-pixels arranged in a regular matrix. So how is it that cinema screens, which are often hundreds of inches or even larger, still maintain such a delicate and smooth visual experience?

Many people assume that this is because cinemas use screens with higher resolution. In fact, most cinemas do not use traditional display screens; instead, they use digital projectors to project images onto a screen. What truly determines the image quality is not the screen itself, but a core component inside the projector—only a few centimeters in size yet containing millions of tiny devices—called the DMD.

DMD stands for Digital Micromirror Device, and it is also the core of DLP (Digital Light Processing) technology. Although many people have not heard of it, it has been applied in many different fields—from cinemas and conference projectors to industrial manufacturing and scientific research.

If you take a projector apart, you will find that it does not contain an LCD screen, but rather a chip covered with tiny mirrors. Each mirror on this chip corresponds to one pixel in the final image.

Unlike ordinary mirrors, these mirrors are not fixed but can flip at high speed.

Each micromirror is mounted on an extremely tiny hinge and is driven electrostatically to switch rapidly between two fixed angles. When the mirror faces the projection lens, light is reflected onto the screen, and that pixel is bright. When the mirror tilts to the other side, light is directed to a light-absorbing area, no longer entering the projection lens, and that pixel becomes dark.

Thus, each pixel corresponds to an independently controllable micromirror. The projector controls the states of millions of micromirrors, rearranging the light to form a complete image.

There is a common misconception here. Many people think that because a pixel has only two states—on and off—the image should be only black and white. In reality, the human eye has a certain persistence of vision for rapidly changing light. When a micromirror switches rapidly between bright and dark, the eye does not see each individual flip, but rather perceives an average brightness.

For example, over a very short period, if the mirror reflects light for half the time and is off for the other half, the eye sees approximately 50% gray. If the mirror is on for 80% of the time, the corresponding pixel appears brighter. By adjusting the on-off ratio of each micromirror over a time cycle, rich grayscale levels can be produced.

This control method is commonly known as pulse-width modulation—using time to express brightness, rather than relying on the mirror itself to change its reflectivity.

The formation of color images is a further extension of grayscale control.

For many single-chip DLP projectors, the light source sequentially produces red, green, and blue light. Each color illuminates the DMD chip in turn, and the micromirror array performs grayscale modulation based on the image information for the current color. Because this process repeats extremely quickly, the human eye ultimately perceives a continuous color image, rather than three colors flashing in succession.

In high-end digital cinema projectors used in theaters, there are also solutions that use three DMD chips, each responsible for one of the red, green, or blue color channels. This avoids the temporal loss caused by sequential color switching, improves light utilization efficiency, and further enhances color performance. This is one of the major technical paths long adopted by digital cinemas.

Since each micromirror corresponds to a pixel, why is it that the cinema screen still shows no visible pixelation?

The answer is not solely about resolution.

First, modern digital cinema projection equipment typically has relatively high image resolution. When millions of pixels are evenly distributed across a screen over ten meters wide, the actual size of each pixel becomes very small. At a normal viewing distance, the human eye often cannot distinguish individual pixel structures.

On the other hand, the DMD chip itself has a high fill factor.

Fill factor can be understood as the proportion of the chip area actually occupied by mirror surfaces that reflect light. If there are large gaps between mirrors, a grid-like structure—commonly known as the "screen-door effect"—can appear in the image. With advances in microfabrication, the micromirrors on modern DMD chips are arranged more and more tightly, and the gaps between them continue to shrink. As a result, the final image appears more continuous, making pixel boundaries even harder to notice.

In addition, the viewing distance in a cinema also plays a significant role. Human visual resolution has a certain limit. When the angle subtended by a single pixel is small enough, even though the pixel exists, the human eye cannot distinguish it from the surrounding pixels. Thus, at an appropriate viewing distance, the audience perceives a continuous and smooth image, rather than a picture stitched together from countless tiny squares.

In fact, most display devices we interact with every day leverage fundamental properties of the human visual system. Whether it is a phone, a television, or a cinema screen, they are all ultimately composed of discrete pixels. It is only through the combined effects of resolution, display method, and viewing distance that people perceive a continuous image.

At this point, many people might think that the DMD is just a component used in cinemas. In reality, its capabilities go far beyond playing movies. Because what the DMD actually controls is not images, but light. It can precisely steer each beam of light according to digital signals, directing it to specific locations or keeping it away from certain areas. This means that wherever spatial modulation of light is required, the DMD has the potential to play a role.

For this reason, it has gradually entered many fields, including industrial manufacturing, biomedicine, semiconductor processing, and 3D metrology.

Among these, maskless lithography is one of the more widely applied technologies in recent years. Traditional lithography typically requires the fabrication of a photomask. A photomask can be thought of as a template with a pattern engraved on it. Light passes through the mask, projecting the pattern onto the surface of a material, which is then processed through subsequent steps to form the desired structure. This approach has been widely used in semiconductor and micro/nanofabrication. However, for R&D, small-batch prototyping, or scenarios where patterns need to be changed frequently, each new mask requires additional time and cost.

DMD-based maskless lithography takes a different approach.

Because each micromirror can be controlled independently, the entire micromirror array essentially functions as a digital mask that can be updated in real time. After a pattern is generated by a computer, there is no need to fabricate a physical mask. The digital pattern is simply sent to the DMD, and the micromirror array controls the light according to the specified state, projecting the corresponding pattern onto the photoresist surface.

If the circuit layout, pattern, or structural design needs to be modified, only the digital file needs to be updated to perform a new exposure—without the need to reprocess a physical mask.

Currently, DMD-based maskless lithography has been applied in research areas such as microfluidic chips, MEMS devices, optoelectronic structures, and biochips. Different experimental needs may require different exposure light sources, optical systems, and process flows, so specific equipment is typically configured according to actual requirements.

The ZEPTOOLS DMD maskless lithography system is also designed based on this digital light modulation approach. The system uses a DMD chip to digitally control exposure patterns, enabling rapid pattern switching. It is suitable for research institutions and university laboratories that require frequent design adjustments. The entire exposure process does not require fabricating physical masks, allowing researchers to continuously modify patterns according to experimental needs, thereby improving flexibility during the R&D process.

From playing a movie in a cinema to fabricating structures at the micron scale—or even smaller—in a laboratory, these may seem like completely different industries. One pursues visual experience, while the other serves scientific research. Yet both rely on the same core capability: using millions of high-speed flipping micromirrors to precisely control light.

For the audience, these micromirrors are hidden inside the projector, and few people ever notice their existence. For researchers, they have become an important part of digital optical systems, giving an ordinary beam of light the ability to work according to a designed pattern. They allow cinematic images to be presented delicately to viewers, and they also enable digital patterns to be accurately projected into the microscopic world in the laboratory.

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