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Camera Sensors: Need To Know How Are They Made?

Camera Sensors: Need To Know How They Are Made?

Do you ever wonder how cameras work, from fancy cameras costing up to $20K to the small camera in the back of your phone?

Let’s find out!

History

One technology from the 19th century has fundamentally changed how we record moments.

Joseph Nicephore Niepce, who had been working with photographic processes since 1813, was the first to create the camera in 1816.

The first image ever captured was the scene from his window at Le Gras in 1826, and it was captured on a sheet of paper covered in bitumen (a type of natural tar). Heliography is the name he gave to his method since it involves exposing light to produce pictures.

It required 8 hours to expose and produced a hazy image that, if not for the date “1826” printed in the bottom left corner, would have been mistaken for an abstract artwork.

Niépce’s work was enhanced by Louis Daguerre, whose contributions resulted in the invention of photography as we know it today, which they called a daguerreotype at that time.

Digital Imaging

Steven Sasson, an engineer with Eastman Kodak, created the first real digital still camera in 1975. A movie camera lens, a few Motorola components, 16 batteries, and some recently developed Fairchild CCD electronic sensors were used to construct his prototype.

The final camera is the same size and weight as a printer. It required Sasson and his colleagues to create a customized screen solely to see the black-and-white images that were captured on a digital cassette tape.

There are 48-megapixel and 12-megapixel cameras in the current Apple iPhone 14 series. 48 and 12 million pixels are contained in that picture. The Kodak prototype featured a 0.01 megapixel resolution. Additionally, taking the first digital picture took 23 seconds.

How Do Modern Camera Sensors Work?

In 1963, the complementary metal oxide semiconductor sensor (CMOS) was invented. However, it wasn’t until the 1990s that it started to be widely employed for imaging applications. In a CMOS sensor, the charge from the photosensitive pixel is converted to a voltage at the pixel site, and the signal is multiplexed by row and column to many on-chip digital-to-analog converters (DACs).

CMOS is a digital device by default. To perform the tasks of resetting or activating the pixel, amplification and charge conversion, and selection or multiplexing, each site essentially consists of a photodiode and three transistors. Due to fabrication irregularities in the numerous charge to voltage conversion circuits, this results in the high speed of CMOS sensors, but also low sensitivity and high fixed-pattern noise.

When the Casio QV-10 added an LCD screen to the rear in 1995, the design of modern digital cameras as we know them changed. The screen measured 46mm (1.8 inches) from corner to corner.

The lens of the QV-10 may also be turned. A semiconductor memory that could hold 96 color still photos was used to save the images after they were taken using a 1/5-inch CCD with 460 x 280 pixels. Auto exposure, self-timing, and close-up macro shooting were some of the other now-standard features. The cost was $1000.

The VideoMan, the first webcam, was introduced by Logitech in 1995.

Sensor Parts

Pixel

A camera sensor’s pixels are a matrix of small potential wells that gather light that comes from an image. These little discrete pixels make up the entire picture. A monitor will display the information that has been gathered, arranged, and transmitted from these sites. The pixels might be, for example, photodiodes or photo capacitors, which, by spatially limiting and storing light, produce a charge proportional to the quantity of light incident on that specific area of the sensor.

Sensor Size

The size of a camera sensor’s active area has a significant impact on the system’s field of view (FOV). When the imaging lens’s fixed main magnification is used, larger sensors produce wider FOVs. It’s crucial to note that the actual sizes of the sensors vary since the nomenclature of these standards is derived from the Vidicon vacuum tubes used in television broadcast imagers.

Frame Rate & Shutter Speed

The frame rate is the number of full frames that are created in a second. For example, a 30 frame per second analog camera has two 1/60 second fields. It is beneficial to use a higher frame rate for high-speed applications in order to capture more photos of the item as it passes through the field of view (FOV).

Next time you take a picture of your lunch, you will know how cameras work.

Understanding the Intricacies of Camera Sensor Manufacturing

Modern camera sensors are complex devices, and their manufacture is a fascinating blend of precision engineering and cutting-edge science. Here, we dive deeper into how these essential components of digital cameras are crafted.

The Manufacturing Process

1. Wafer Fabrication

The journey of a camera sensor starts with the creation of a silicon wafer. Silicon, derived from quartz sand, is purified and melted into a cylindrical silicon ingot, which is then sliced into thin wafers. These wafers serve as the substrate on which sensor circuits are built.

2. Photolithography

This process involves transferring the sensor’s circuit pattern onto the wafer. The wafer is coated with a light-sensitive chemical called photoresist. It is then exposed to ultraviolet light through a photomask, which hardens the pattern onto the wafer. The unexposed photoresist is washed away, leaving the circuit design etched into the wafer.

3. Doping

To modify the electrical properties of the silicon wafer, a process called doping is used. Impurities are introduced to the silicon, which can create either an excess or a shortage of electrons, thus forming N-type and P-type silicon layers. This step is crucial for the creation of photodiodes that are sensitive to light.

4. Etching and Deposition

After doping, the wafer undergoes further etching to remove unwanted materials and deposition to add different layers. These layers are crucial for forming the actual electronic circuits and photodiodes.

5. Passivation Layer

A passivation layer is added to protect the delicate structures on the wafer from environmental damage and to prevent the circuits from shorting out.

6. Assembly

Once the wafers are processed, they are cut into individual chips. These chips are then mounted onto a sensor package that protects them and connects them to the camera system.

7. Testing and Calibration

Every sensor is rigorously tested for defects and calibrated for optimal performance. Calibration involves adjusting the sensor’s properties to ensure accurate colour reproduction and exposure.

Key Technologies in Sensor Development

Micro-Lens Arrays

One significant advancement in sensor technology is the use of micro-lens arrays. Each pixel on a sensor is equipped with a tiny lens that focuses light more efficiently into the photodiode. This technology significantly enhances the sensor’s ability to capture light, improving image quality, especially in low-light conditions.

Back-Illuminated Sensors

Traditionally, sensors were front-illuminated, meaning that light had to travel through the wiring before reaching the photodiode. Back-illuminated sensors flip this design so that light hits the photodiodes directly, greatly increasing the amount of light captured and enhancing the sensor’s sensitivity.

Colour Filter Arrays

Most sensors use a Bayer filter mosaic, which consists of alternating patterns of green, red, and blue filters over the pixels. This setup allows the sensor to capture colour information by filtering different wavelengths of light into the corresponding photodiodes. The camera’s image processor then reconstructs a full-colour image from this data.

The Impact of Sensor Technology on Photography

The advancements in sensor technology have profoundly impacted photography, enabling cameras to become smaller, faster, and capable of capturing images with astonishing detail and low noise. This progress has democratized photography, making high-quality imaging accessible to professionals and amateurs alike.

Conclusion

From the early days of film to the sophisticated digital sensors of today, the evolution of camera technology continues to push the boundaries of what can be captured and preserved in an image. Each component in a camera sensor, from the photodiodes to the micro-lenses, plays a crucial role in transforming light into the vivid images we see on our screens and in print. The next time you snap a photo, remember that it’s not just a simple click of a button, but a marvel of modern engineering and decades of innovation.

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