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Breakdown occurs always at the same, precise values of voltage. As a result, an intense electric field exists within the depletion region. B. zener mechanism C. both zener and avalanche mechanism D. none of the above . ADD COMMENT 0. written 2.3 years ago by sashivarma58 • 180: It occurs in a reverse biased p-n diode when the electric field enables tunnelling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers which suddenly increase the reverse current. Zener Voltage V Z Manufacturers specify the value of breakdown voltage V B, also known as the zener voltage V Z at specific value of test current, Zener diodes are available for value of V Z from 2.5 volts to over 500 volts with accuracies between 5% to 20%.. Power Dissipation It is the product of V Z and I Z.The maximum power rating varies from 150 mW to 250 watts. zener breakdown mechanism • 9.2k views. When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. The mechanism was first discovered by a man named Zener. We identified the degradation mechanisms so as to design a reliable protection diode with improved robustness and able to sustain at least 1000 ESD stresses over the product lifetime. Ie electrons on p side and holes on n side attains high velocity. 191. This causes a very thin depletion region. Zener breakdown occurs in a zener diode at low reverse voltages. One is called zener breakdown and the other is called avalanche breakdown. Breakdown is characterized by the rapid increase of the current under reverse bias. The zener breakdown voltage of the zener diode is depends on the amount of doping applied. An experimental study has been made on the breakdown characteristics of alloyed germanium p+-n junctions. There are two mechanisms by which breakdown can occur when PN junction is Reverse bIased: 0. The 2D extent of the p+ region is controlled by the etch coordinate of an oxide mask. They are (i) avalanche breakdown and (ii) zener breakdown. Breakdown characteristics are found to be co… In the off-state in which Si-based Lateral Double-diffused MOS (LDMOS), SiC-based Schottky Barrier Diode (SBD), the PN junction and gate Schottky junction are reverse-biased, avalanche breakdown is responsible for the breakdown. Avalanche and Zener breakdown both occur in diode under reverse bias. This paper reviews the physical breakdown mechanisms of Si-, SiC- and GaN-based power semiconductor devices. Heavily doped diodes can undergo a different kind of breakdown. (i) Avalanche breakdown : When both sides of the PN junction are lightly doped and the depletion layer becomes large, avalanche breakdown takes place. Although all PN junctions exhibit a voltage breakdown, it is important to know that there are two distinct voltage breakdown mechanisms. Two distinct mechanisms have been suggested for this sudden increase. Zener Breakdown Diode. mechanisms of ESD protection diodes subjected to system level ESD stresses. Zener diodes are available with zener voltages in the range of 1.8V to 400V. In the absence of an external field, the few electrons in the upper band are in the lowest energy state of this band; under the action of an electric field, they are raised to higher levels. So, … Breakdown mechanisms . what is Zener breakdown. The avalanche breakdown occurs because of the ionization of electrons and hole pairs whereas the zener breakdown occurs because of heavy doping. View Answer. There are two mechanisms which give rise to the breakdown of a PN junction under reverse bias condition. Silicon and Germanium both can be used for the construction of Zener diode, but Silicon is often used because of it can operate at higher temperature, and current capability of silicon is high. One is called zener breakdown and the other is called avalanche breakdown. A short diffusion is performed in Athena to drive in the p+ dopant. View Answer. Zener Break Down Diode. The breakdown is either due to the Zener breakdown effect that occurs below 5.5 V, or impact ionization that occurs above 5.5 V. Both mechanisms result in the same behavior and do not require different circuitry; however, each mechanism has a different temperature coefficient. In the Zener breakdown mechanism, the electric field becomes as high as 10 7 V/m in the depletion layer with only a small applied reverse bias voltage. On the other hand, Avalanche Breakdown occurs in the device due to the collision of electrons moving at high speed. Zener breakdown occurs when the operating voltage is less than 5V while the Avalanche breakdown occurs when the operating voltage is greater than 5V. Once the voltage across a Zener reaches the breakdown voltage, it is said to be Zener diode’s Zener voltage VZ. Hence the result will be in the force of attraction to the negatively charged electrons nearby the junction. A. avalanche B. zener C. both avalanche and zener D. none of the above . Discuss in Forum . So high reverse bias causes increase in velocity of minority carriers. Although there are two types of breakdown mechanism, still only name Zener is preferred. So this mechanism is also called, Zener breakdown and the diodes are called Zener diodes. In this video let's explore what happens in a very heavily doped diode. If the reverse voltage is increased in the PN junction diode thus the electric field near the diode junction increases. 4.5.1. A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". Near the zener breakdown voltage (V), the field is intense enough to pull electrons from their valence bands and create current. When looking at the equation describing current in a diode, only the forward current is considered; the reverse current resulting from breakdown in the diode is not present in this equation. Sze. The Zener Breakdown and Avalanche Breakdown are two different mechanisms by which a PN junction breaks. The avalanche breakdown which is the breakdown mechanism in most of the breakdown diodes and zener diodes, occurs at 6 volt or more. The voltage across reverse Biased PN junction increase to a certain value, called breakdown voltage, the high reverse current is caused which may damage the junction diode.. Zener breakdown. 2.2 Zener breakdown With increase in doping concentration the breakdown mechanism, changes from Avalanche to a tunneling mechanism. On the other hand, if the diode is lightly doped, the zener breakdown occurs at high reverse voltages. Zener breakdown occurs in heavily doped junctions in which the transition from the p side to the n side is very abrupt. A zener diode that has very narrow depletion layer will breakdown by mechanism. Breakdown voltage of Zener diode. In Zener breakdown, the increase in reverse voltage causes the expansion of the depletion layer. BREAKDOWN MECHANISMS Figure 3 depicts the extension of reverse biasing to the point where voltage breakdown occurs. In this process, it became possible for some of the electrons to jump across the barrier from the valence band in p material to some of the unfilled conduction band in n material. Zener Diode Specifications. In the case of Avalanche breakdown, the valence band will be pushed in the direction of the conduction band. Zener breakdown occurs when the high electric field is created across the junction. In lightly doped pn junction depletion region width is more. For AlGaN/GaN high electron mobility … Although all PN junctions exhibit a voltage breakdown, it is important to know that there are two distinct voltage breakdown mechanisms. This equation is valid only for values of V r smaller than V br. At high reverse bias, the exact mechanism that creates breakdown and drives current flow is different in various diodes (pn diode, Schottkey, or Zener). Zener diodes These can be made to conduct in reverse bias (backward), and are correctly termed reverse breakdown diodes. Adapted from Physics of semiconductor devices - S.M. Zener diodes, on the other hand, are designed to operate in the breakdown region (provided the current does not become too excessive) and recover completely when the applied reverse voltage changes to less than the breakdown voltage. Zener breakdown: Zener breakdown is observed in Zener diode having vz less than 5-volt aur between 5 to 8 volt let’s understand the Zener breakdown mechanism for Vz less than 5 volts. In zener breakdown the value of breakdown voltage … The studied devices and the applied ESD stress are presented in section II. mechanism changes to a Zener breakdown process. If the diode is heavily doped, zener breakdown occurs at low reverse voltages. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. BREAKDOWN MECHANISMS Figure 3 depicts the extension of reverse biasing to the point where voltage breakdown occurs. The force from this junction will free electrons from the covalent bond and moves the free electrons to conduct the band. As the junction temperature increases, the voltage breakdown point for … 192. This effect called Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. A Zener diode can use any of these two breakdown mechanisms. Definition of Zener Tunneling: It is a reverse breakdown mechanism in which high electric field generated at P-N junction, electrons tunnel from the valence band to conduction band of a semiconductor device. value of V r to V br, higher is the reverse bias current. If the breakdown occurs at higher voltages (from a few volts to hundreds of volts), the mechanism is avalanche breakdown. The breakdown voltage is a key parameter of power devices. Although the Zener breakdown mechanism is a significant contributor only at lower levels of V Z, this sharp change in the characteristic at any level is called the Zener region and diodes employing this unique portion of the characteristic of a p-n junction are called Zener diodes. It's a quantum mechanical effect. General breakdown characteristics: The maximum reverse bias voltage that can be applied to a p-n diode is limited by breakdown. Of these, the first is a process analogous to the electrical breakdown of gases. The voltage that Zener diode drops across itself will not continue to increase. Discuss in Forum . The crucial difference between the Zener and Avalanche breakdown is the operating mechanism. Advantages of zener diode. Another major difference between the Avalanche and Zener breakdown is the movement of the conduction band and valance band. A zener diode is heavily doped to reduce the breakdown voltage. 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