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Diode Parameter

Symbol

Definition

(Avalanche) Breakdown Voltage

V_B or V_BR

The reverse bias voltage at which a diode junction enters avalanche breakdown. For most types of RF and microwave diodes, this region of operation is to be avoided.

(Minority)(Carrier) Lifetime

T_L or t

The mean time a free charge carrier exists in a diode junction immediately after its bias has transitioned from a forward bias current to a reverse bias voltage. Minority carrier lifetime is related to the amount of charge a diode stores while forward biased and is typically defined for a specific combination of forward bias current and peak reverse current.

Capacitance Ratio

C_Tx/C_Ty

The ratio of the capacitance a diode produces with applied reverse bias voltage V_X to its capacitance with applied reverse bias voltage V_Y

Forward Bias Voltage

V_F

Voltage polarity which is applied to a diode junction which produces current flow. For example, the positive side of a voltage connected to the anode of a diode and the negative side of the voltage applied to the diode’s cathode is the forward bias condition.

Forward Current

I_F

The current that flows in a diode when a forward bias voltage is applied.

I Layer Length

W

Also known as I layer width. The mechanical thickness of the intrinsically-doped layer of a PIN diode. This parameter heavily influences many of the electrical properties of a PIN diode, including switching time, distortion performance, series resistance, capacitance, etc.

Junction Capacitance

C_J

The capacitance of a diode which results from the diode’s depletion region acting as dielectric layer separating two conductive regions, the anode and the cathode layers. This capacitance is produced by the semiconductor die only.

PIN (or p-i-n) Diode

A three-layer diode, consisting of a heavily-acceptor-doped anode layer and a heavily-donor-doped cathode layer sandwiched around a very lightly-donor-doped layer known as the intrinsic layer

Reverse (Leakage) Current

I_R

The current that flows between a diode’s anode and cathode terminals when a reverse bias voltage is applied. This is a non-ideal characteristic of a semiconductor diode and is generally orders of magnitude larger than reverse saturation current.

Reverse Bias Voltage

V_R

The voltage polarity which is applied to a diode junction to prevent current flow. For example, the positive side of a voltage source connected to the cathode of a diode and the negative side of the voltage source applied to the diode’s anode is the reverse bias condition.

Reverse Recovery Time

T_RR

The interval required for the reverse bias current to substantially decay, immediately after the forward bias current is changed to a reverse bias voltage. T_RR is similar in concept to T_L. The primary difference is the magnitude of the forward and reverse biases are typically much larger for T_RR than for T_L measurements.

Reverse Saturation Current

I_S or I_O

The tiny current which flows when semiconductor diode junction is under reverse bias. This current comprises thermally-generated free minority carriers (electrons in the anode layer, holes in the cathode layer) which flow in the reverse bias direction. This current is temperature dependent and its magnitude is typically in the nanoamperes order of magnitude.

Schottky Diode

A diode whose rectifying junction is formed by intimate contact of a metal and a doped semiconductor. A Schottky diode operates with majority carriers only.

Series Resistance

R_S

For PIN diodes: The RF resistance presented primarily by the diode’s I-layer as a function of a specified DC forward bias current

For Schottky diodes: The slope of the diode’s current vs. voltage characteristic at a specified forward bias current

For Varactor diodes: The RF resistance presented primarily by the diode’s un-depleted cathode layer as a function of a specified DC reverse bias voltage

Total Capacitance

C_T

The parallel combination of a semiconductor diode’s junction capacitance (C_J) and the parasitic capacitance of a package in which the die resides.

Varactor Diode

A pn junction device whose cathode layer has a tightly controlled doping concentration. The thickness of the diode’s depletion layer is a function of the magnitude of the applied reverse bias voltage, the area of the diode’s junction and the doping concentration of the cathode layer.