CRTs Brought Technology to Life for a Century

AS PETER KELLER INTRODUCED IN THE JUNE 1997 ISSUE OF Information Display, “In 1897, Karl Ferdinand Braun invented a device that changed the world.”¹ That 1997 issue commemorated the 100th anniversary of the invention of the cathode-ray tube (CRT). Those of you who have entered our industry within the last 20 years have probably only had a passing exposure to what was once the greatest electronic display technology of our time. But for many of us, the CRT and all the electronics to support it were the big leagues of display engineering.

The idea for the CRT came from experiments that showed the luminescence of gases in the imperfect vacuums of early experimental tube devices, or the fluorescence of their glass walls indicated the presence of the mysterious “cathode ray,” which was energy from a beam of electronics moving from a cathode at one end to a positively charged anode at the other end. Soon scientists found that those beams could be deflected by magnetic fields, carried energy, and could cause a surface coated with phosphors to glow when they came in contact.

Braun disclosed his CRT design in 1897. His innovation, known as the “Braun Tube,” included implementing a phosphor surface on the face of the tube made from a transparent sheet of mica (Fig. 1). The electron beam struck the phosphor and produced a visible spot. An electromagnetic coil next to the neck of the tube produced a vertical deflection of the beam. The measured voltage was applied to the coil and resulted in a green line of ∼25 mm in length on the screen. A rotating mirror in front of the screen—as used with mechanical oscillographs of the time—provided scanning in the horizontal axis to allow the waveshape to be observed. From this, a version of the modern oscilloscope display was born (although the actual term oscilloscope reportedly was not introduced until a paper published in 1927). Later experiments added a second deflecting coil at a right angle to the first, allowing the beam to be moved anywhere on the face of the tube.

Additional innovations in the CRT included the discovery of the oxide-coated hot cathode, which allowed for a much more efficient source of free electrons for the beam and greatly reduced the total anode voltage required. The design of the modern electron gun with focusing elements had the ability to modulate the beam's energy dynamically during scanning. With these features, the modern monochrome television tube was born, and the systems to produce television images progressed rapidly from the 1920s to 1930s.

By the late 1930s, commercial CRTs by RCA, Cossor, DuMont, Telefunken, and others were commercially available and were being employed in limited quantities for oscillographic and television applications (Fig. 2). The stage was set for the rapid growth and refinement that was to come as the CRT was drafted for military electronics and radar applications during World War II. In 1939, approximately 50,000 CRTs were produced; by the end of 1944, that number grew to more than 2 million per year.

RCA's first public demonstration in 1950 of the shadow-mask color picture tube marked the beginning of color imaging. By the early 1960s, the three-beam shadow-mask design was the foundation for all future innovations and most applications, except for projection that relied mostly on three individual monochrome CRTs of red, green, and blue.

Through the second half of the 20th century, a whole supply and manufacturing infrastructure existed to support CRT—electronics, yolks, phosphors, glass tubes, exotic materials, test equipment, and much more. A significant aspect of that supply chain was the glass bulb. In September 1993, ID published an important story by Robert L. Mathew from Corning about the history of the bulb that forms the CRT.³ Corning's role in innovating the CRT began around 1935 with requests to make TV and radar bulbs. At that time, it was believed that 12 inches was the largest size anyone would want or that could be mass produced.

While RCA worked on metal and glass hybrid tubes, Corning continued to develop all-glass tubes, and by the mid-1950s, 27-inch faceplate glass tubes were in production. Glass tubes became the dominant platform for most applications, and the efforts of Corning included further innovations such as centrifugally casting the funnel, electric sealing of the panel and funnel, the multiform process for producing intricately shaped glass parts for the CRT electron gun, the anode button, barium glass, and frit-sealing system. By 1990, more than 2 billion CRTs had been manufactured worldwide.

In 1997, the CRT was still the dominant platform for desktop monitors and TVs, although plasma and LCD flat panels were beginning to gain ground. There was ongoing engineering progress in the performance of CRTs, as Hsing-Yao (Jimmy) Chen described in his June 1997 article.⁴ He reviewed the most fundamental advances in electron gun designs and highlighted a pair of papers published at Display Week 1996 that continued to improve as well as simplify electron gun design. CRTs were not ready to fade into the dark. The venerable CRT held on for a long time after its 100th anniversary was celebrated (Fig. 3).

Most of this information was sourced from the June 1997 issue of ID, which commemorated the anniversary of CRT. Some also came from the September 1993 story about Corning's history with CRTs, and the July 2012 issue highlighting CRTs as part of SID's 50th anniversary. This content and much more can be found in our archives at archive.informationdisplay.org.

After the January/February 2024 “Looking Back” story that recalled the 100th anniversary of liquid crystals, we received some reader feedback. We noted that the discovery of the dynamic scattering mode published by George Heilmeier in 1967 enabled the development of LC displays. However, as Professor Shin-Tson Wu thoughtfully pointed out, although Heilmeier made an important contribution, his light-scattering mode by itself would not have enabled the wide-ranging success LCDs achieved. The next important advance was the field effect invented by Wolfgang Helfrich and Martin Schadt in 1970.⁵

In addition, the July 2012 article, “A Brief History of Key Areas in Display Technology” summarizes the contributions of many other scientists in the field of LCDs.⁷ These contributions are well worth your time to browse. There is always more to the story, and we will strive not to leave out the most important bits in the future.