Schottky diode

Tuesday, 02 January 2007

Schottky diodes are semiconductor devices which have a metal-semiconductor transition as their basic structure and whose basic electronic properties are defined by this transition. Diodes are a fundamental electronic building block. Their ability to restrict current flow to substantially one direction is a critical property relied upon in virtually every electronic circuit manufactured, from the smallest power supply to the largest industrial process controller. In recent years, mobile communication equipment such as digital cellular phones and high-speed data communication equipment have been required to be small, thin and lightweight, low power consumption, a high frequency, and multi bands. For this reason, a high-frequency module such as an antenna switch module and a voltage controlled oscillator module and the like constituting a key component in the above-mentioned mobile communication equipment and high-speed data communication equipment and the like has been smaller, thinner and more lightweight. In response to reduction in the size of the high-frequency module, various diodes including a variable capacitance diode, a PIN diode, a Schottky diode used in the high-frequency module are required to be small. Schottky diodes have been used for many years in the semiconductor industry in, for example, electronic systems, such as amplifiers, receivers, control and guidance systems, power and signal monitors, and as rectifiers and clamps in RF circuits. Commercial applications include radiation detectors, imaging devices, and wired and wireless communications products. Typically, a Schottky diode consists of a metal layer connected to a doped semiconductor layer. The Schottky barrier is formed at the juncture of the metal and the semiconductor. Due to radius of curvature effects at the edges of the Schottky barrier, a field quickly builds up when a reverse bias is applied. This leads to a low breakdown voltage and poor leakage characteristics.

A Schottky diode can be formed by the connection of a metal or silicide layer to a doped semiconductor layer. A Schottky junction (or Schottky barrier) is formed at the junction of the metal layer and the doped semiconductor layer. Typically, a separate metallization layer is insulatively disposed over the substrate to provide an electrical contact to the Schottky contact layer. Optionally, a separate diffusion barrier layer can be interposed between the metallization layer and the underlying Schottky contact layer to prevent interdiffusion of the metallization layer with the Schottky contact layer and the semiconductor substrate. Schottky diodes have a metal-semiconductor transition as their basic structure and whose basic electronic properties are defined by this transition. A Schottky diode is formed from a semiconductor-metal combination which is chosen such that a depletion zone arises at the boundary surface. The current-voltage characteristic of this arrangement depends on the polarity of the applied voltage. A Schottky diode is characterized by a low turn-on voltage, fast turnoff, and nonconductance when the diode is reverse biased. To create a Schottky diode a metal-silicon barrier must be formed. In order to obtain the proper characteristics for the Schottky diode, the barrier metal is likely different than the metal used in other process steps such as metal ohmic contacts. When forward biased, a Schottky diode provides a low-resistance current path and, when reverse-biased, a high-resistance current path. On the other hand, the metal contact, which is formed on the heavily-doped region, has a current-to-voltage (I/V) relationship that is linear or resistive. A Schottky diode is primarily a majority carrier device. Under many circumstances (primarily low injection conditions), current is conducted primarily by majority carriers. As a consequence, Schottky diodes often have faster switching times than p-n junction diodes of comparable size. The voltage-current characteristics of Schottky diodes are very similar to the voltage-current characteristics of p-n junction diodes. Schottky diodes can be switched from one state to another, either from on to off or from off to on much faster that p-n junction diodes. The performance of the Schottky diode is typically gaged by the product of its series resistance and its junction capacitance. This product must be minimized for the best performance to be achieved. Unguarded Schottky diodes typically have poor reverse leakage and poor breakdown characteristics. To improve leakage characteristics, high performance Schottky diodes are provided with junction guard rings. Guard rings provide excellent breakdown characteristics in both forward and reverse bias.

Schottky barrier diodes are widely used in integrated circuits in applications such as decoupling devices in digital circuits (silicon bipolar and gallium arsenide MOSFET) and as clamping devices to prevent heavy saturation of bipolar transistors. Schottky diode is an important power device and used extensively as output rectifiers in switching-mode power supplies and in other high-speed power switching applications, such as motor drives, switching of communication device, industry automation and electronic automation and so on. Schottky diodes are widely used as voltage rectifiers in many power switching applications, such as switching-mode power supplies, electric motor, switching of communication device, industry automation and electronic automation. The use of a Schottky diode generally allows integrated circuits to have greater speed because it is a majority carrier device. Having a low carrier lifetime attributes to its greater switching speeds. When incorporated into integrated circuit (IC) technologies the Schottky diode enhances the range of diodes available. The Schottky diodes have lower turn-on voltages because of the lower barrier height of the rectifying metal-to-semiconductor junction and have faster switching speeds because they are primarily majority carrier devices.

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