Schottky Diode

Schottky Diode is a type of metal-semiconductor diode with low forward voltage drop and very fast switching speed.

Schottky Diodes, like other diodes, are a type of semiconductor that can be used in a variety of applications, such as forming, switching and trimming.The main advantage is that the forward voltage drop of the Schottky Diode is significantly less than the 0.7 volt of the traditional silicon pn-connection diode.

Schottky diodes have many useful applications, from straightening, signal conditioning and switching to TTL and CMOS logic gates, mainly due to low power and fast switching speeds.TTL Schottky logic gates are defined by the letters LS that appear somewhere in the logic gate circuit codes, for example 74LS00.

PN-connection diodes are created by combining a p-type and an n-type semiconductor material that allows it to be used as a rectifier device, andWe found that when polarized, the depletion zone decreased greatly, allowing the current to flow through it. when forward and reverse polar, the depletion zone is increased and the current flow is blocked.

Using an external voltage to direct the pn-link forward or backward, the polarity action reduces or increases the resistance of the connection barrier, respectively.Thus, the voltage-current relationship (characteristic curve) of a typical pn-connection diode is affected by the resistance value of the connection.Note that the pn-connection diode is a nonlinear device, so dc resistance will vary according to both the pre-voltage and the current passing through it.

When polarized forward, transmission via connection does not start until the external polarization voltage reaches the "knee/elbow voltage", where the point current increases rapidly, and the voltage required for forward transmission for silicon diodes is around 0.65 to 0.7 volts, as shown.

Schottky Diode
PN-link Diode IV-Features

For practical silicon connection diodes, this knee/knee voltage can be anywhere from 0.6 to 0.9 volts, depending on how it is contributed during production and whether the device is a small signal diode or a much larger rectifier diode.The knee voltage for a standard germanium diode is about 0.3 volts or much lower, making it more suitable for small signal applications.

Schottky Diode

Unlike a traditional pn-connection diode consisting of a piece of P-type material and a piece of N-type material, Schottky Diodes are made using a metal electrode connected to an N-type semiconductor.Since they are made using a metal compound on one side of their connection and additive silicon on the other, the Schottky diode therefore has no layers of depletion and is classified as unipolar devices, unlike typical pn-link diodes, which are bipolar devices.

The most common contact metal used in schottky diode construction is "Silicide", a highly conductive compound of silicon and metal.This silicide metal-silicone contact is<0,4V civarında daha küçük bir ileri voltaj düşüşü üreterek daha fazla akımın akmasına izin veren oldukça düşük bir omik direnç değerine sahiptir.Different metal compounds will typically produce different forward voltage drops from 0.3 to 0.5 volts.

Schottky Diode Structure and Symbol

Schottky Diode
Schottky Diode Structure and Symbol

Above is the simplified structure and symbol of a Schottky diode, in which a slightly additive n-type silicon semiconductor is combined with a metal electrode.

The width and therefore electrical properties of this metal-semiconductor connection will depend greatly on the type of metal compound and semiconductor material used in its structure, but when forward-oriented, electrons move from n-type material to metal electron, allowing the current to flow.

Since there are no P-type semiconductor material and therefore minority carriers (holes), the transmission of diodes stops very quickly when inverted and blocks the flow of current, as in a traditional pn-connection diode.Therefore, for a Schottky diode, a very quick response is given to changes in deviation and the rectifier shows the properties of the diode.

As discussed earlier, the knee voltage at which a Schottky diode becomes "ON" and begins to transmit is at a much lower voltage level than the pn-connection equivalent, as shown in the following IV characteristics.

Schottky Diode IV-Features

Schottky Diode

As we can see, the general shape of metal-semiconductor Schottky diode IV characteristics is very similar to a standard pn-connection diode, except for the corner or knee voltage that the ms-connection diode begins to transmit.

Due to this low value, the forward current of a silicon Schottky diode can be many times larger than that of a typical pn-link diode, depending on the metal electrode used.

However, the reverse leakage current is generally much larger for pn-diode (for IR, Schottky diode).

However, if the characteristic curve iv shows a more nonlinear rectifier characteristic, then this is an Ohmic contact.Ohmic contacts are widely used to connect semiconductor chips and chips with external connection pins or circuits of a system.For example, connecting the semiconductor chip of a typical logic gateway to the pins of a plastic double-row (DIL) package.

Also, due to the fact that schottky diode is produced by metal-semiconductor connection, it tends to be slightly more expensive than standard pn-connection silicon diodes with similar voltage and current properties.For example, the 1.0 Amperage 1N58xx Schottky series is compared to the general purpose 1N400x series.

Schottky Diodes at Logic Gates

Schottky diode also has many uses in digital circuits and is widely used in Schottky transistor-transistor logic (TTL) digital logic gates and circuits due to higher frequency responses, reduced switching times and lower power consumption.Where high-speed switching is required, Schottky-based TTL is the obvious choice.

Schottky TTL has different versions, all with different speeds and power consumption.The three main TTL logic series using the Schottky diode are given as follows:

  • Schottky Diode Clamped TTL (S series) – Schottky "S" series TTL (74SXX) is an improved version of the original diode-transistor DTL and transistor-transistor 74 series TTL logic gates and circuits.Schottky diodes are placed in the base-collector connection of switching transistors to prevent them from saturating and creating propagation delays that allow faster operation.
  • Low-Power Schottky (LS series) – The transistor switching speed, stability and power distribution of the 74LSXX series TTL are better than the previous 74SXX series.In addition to higher switching speed, the low-power Schottky TTL family consumes less power, making the 74LSXX TTL series a good choice for many applications.
  • Advanced Low Power Schottky (ALS series) – Additional improvements in materials used to produce MS connections of diodes mean that the 74LSXX series has lower propagation latency and much lower power consumption compared to the 74ALSXX and 74LS series.However, the ALS series is slightly more expensive, as it is a newer technology than the standard TTL and a more complex design internally.

Schottky Compressed Transistor

Schottky Diode

All previous Schottky TTL gateways and circuits use a compressed Schottky transistor to prevent them from being forced to saturation.

As shown, a SchottkyThe compressed transistor is basically a standard bipolar connection transistor with a Schottky diode connected in parallel along the base-collector connection.

When the transistor operates normally in the active region of its characteristic curves, the base-collector connection is inverted, and therefore the diode is inverted to allow the transistor to operate as a normal npn transistor.However, when the transistor begins to saturate, the Schottky diode is polarized forward and clamps the collector-base connection to a knee value of 0.4 volts, keeping the transistor out of hard saturation as any excessive base current is passed through the diode.

Preventing the saturation of switching transistors of logic circuits greatly reduces propagation latency and makes Schottky TTL circuits ideal for use in flip-flops, oscillators and memory chips.

Summarize

Schottky Barrier Diode, also known as Schottky Diode, which we see here, has two major advantages over a metal electrode and an n-type semiconductor traditional Pn-connection diodes; faster switching speed and low-speed pre-voltage voltage.

Metal-semiconductor or ms-connection typically provides a much lower knee voltage of 0.3 to 0.4 volts compared to the 0.6 to 0.9 volts seen in a standard silicon-based pn-connection diode for the same forward current value.

Variations in metal and semiconductor materials used for their structure mean that silicon carbide (SiC) Schottky diodes can be "ON" with an advanced voltage drop as small as 0.2 volts with the Schottky diode replacing the less used germanum diode.

Schottky diodes are rapidly becoming the preferred straightening device in low voltage, high current applications for use in renewable energy and solar panel applications.

However, compared to pn-connection equivalents, Schottky diode reverse leakage currents are larger and reverse fault voltages are lower at about 50 volts.

A lower opening voltage, faster switching time and reduced power consumption make the Schottky diode extremely useful in many integrated circuit applications, the most common of which are 74LSXX TTL series logic gates.

Metal-semiconductor connections can be operated as "Ohmic contacts" as well as rectifier diodes by placing metal electrodes in highly additive (and therefore low resistant) semiconductor regions.Ohmic contacts transmit the current evenly in both directions and allow semiconductor plates and circuits to be connected to external terminals.