Seven Questions Help You Understand LED Chip

This technical article answers seven questions to help people easily understand LED.

1. What is the manufacturing process of LED chip?

LED chip manufacturing is mainly to make effective and reliable low ohmic contact electrode and meet the minimum pressure drop and pressure pad, at the same time produce the light as much as possible. P type used in the general contact metal includes AuBe, AuZn alloy, N surface often uses AuGeNi alloy. Alloy layer formed after coating also need light emitting area as much as possible by lithography process, so as to the left alloy layer can meet effective reliable low ohmic contact electrode and the requirement of the welding line pressure pad. After the photolithography process, it also need alloying process, which is usually carried out under the aegis of the H2 or N2. Alloying time and temperature are usually based on factors such as semiconductor material properties and alloy furnace form. If it is blue, green, or other chips, of course, the chip electrode process is more complex, which needs to increase the passivation film growth.

2. During the manufacturing process, which steps have an important effect on photoelectricity?

In general, after the LED epitaxial production, its main performance has already set, and chip manufacturing will not change its nature, but in the process of coating, alloying inappropriate bad conditions can cause some bad electrical parameters. Low or high alloying temperature can cause ohmic contact undesirable and poor ohmic contact is the main reason for the high pressure drop VF. After cutting, if some corrosion process is carried out on the edge chip, it will be helpful to improve the chip reverse leakage current. This is because with the diamond wheel blade cutting, edge chip will remain more debris powder, which may cause leakage if it adheres to PN, and even has a breakdown phenomenon.

3. Why the LED chip has different sizes? What is the influence？

The LED chip size can be divided into low power chip, medium power chip and high power chip. According to customer requirements it can be divided into single pipe, digital, dot matrix, decorative lighting and other categories. As for the chip specific size, it is decided according to the actual production level of different chip manufacturers, which has no specific requirements. As long as the process passes, small chip can improve unit of output and reduce the cost and the photoelectric performance is not fundamental changed. Chip current is actually associated with current density through the chip, which means the chip is small, so does the current, vice versa, big chip cause large current, and their basic unit current density is almost the same. But considering the heat dissipation is the main problem of the big electricity flow, so its luminous efficiency is lower than the small current. On the other hand, due to the area increasing, the body resistance of the chip will reduce, so the voltage will be dropped.

4. What does the LED high-power chip refer to?

Commonly used high-power white light LED chip in the market can be seen all around 40 mil, and  high power chip power generally refers to the electric power is more than 1w. Due to the quantum efficiency is generally less than 20% and most of the electricity will be converted into heat energy, so it's very important to high power chip cooling and the chip should be large enough.

5. What are the different requirements between producing GaN epitaxial materials chip processing equipment and GaP, GaAs, InGaAlP? Why?

Ordinary LED red or yellow chip, and highlighting quaternary red yellow chip substrate are in compound semiconductor materials such as GaP, GaAs, which is generally used as the N type substrate. Lithography with wet process, and finally blade cut into chips with emery wheel. Blue and green chips of GaN material is used of the sapphire substrate, and due to the sapphire substrate is insulation, so it cannot used as one of the LED, which must pass the dry etching process at the same time adjusts some of the passivation process. Because sapphire is very hard, it is difficult to cross into a chip with emery wheel blade. So its process is more complex than GaP, GaAs materials LED.

6. What are the characteristics of “transparency electrode” structure?

Transparent electrode is to be able to conduct electricity; another one is to be able to pervious to light. This material is now the most widely used in LCD production technology, its name is called indium tin oxide, ITO abbreviations, but it cannot be used as welding pad. Before producing, you should first make ohmic electrodes on the chip surface, and then cover a layer of ITO and then a layer of solder pad. In this way the current down from the lead through the ITO layer evenly distributed to the various ohmic contact electrode, and at the same time because refractive index is between air and epitaxial material refractive index, ITO can improve the light angle and luminous flux can be increased.

7. What is the mainstream of development of semiconductor lighting technology?

With the development of semiconductor LED technology, its application in the field of lighting is more widely; especially the emergence of white LED is becoming a hot spot of semiconductor lighting. But the key chip and encapsulation technology needs to be improved, and in terms of the chip, it should develop to the high power, high photosynthetic efficiency and reduce the thermal resistance. Improve power means the use of the chip current increasing, and the most direct way is to increase the chip size. Now widespread high power chips are around 1mm*1mm, using the current 350 ma. Due to the use of current increases, heat dissipation problems become prominent question, now, through the method of flip chip basically solved the problem. With the development of LED technology, its application in the field of lighting will face an unprecedented opportunities and challenges.