Heterostructure barrier varactor
Encyclopedia
The Heterostructure barrier varactor (HBV) is semiconductor
diode
with an anti-symmetric current-voltage relationship and a symmetric capacitance-voltage relationship, as shown in the graph to the right. The device was invented by Erik Kollberg together with Anders Rydberg in 1989 at Chalmers University of Technology
.
The inset of the figure shows the circuit schematic symbol of the HBV. From the symbol, one can conclude that the HBV consists of two, back to back, anti-serially connected rectifying diodes (such as Schottky diode
s for instance). The gap in the middle of the diode symbol represents the inherent capacitance of the device. The electrical characteristics of the HBV are realized by separating two layers of a semiconductor material (A) with a layer of another semiconductor material (B). The band-gap of material (B) should be larger than for material (A). This results in a barrier for the carriers trying to travel through the layers (A)-(B)-(A). The (A) layers are usually n-doped which means that electrons are the majority carriers of this device. At different bias voltages the carriers are redistributed and the distance between the carriers on each side of the barrier (B) is different. As a consequence the HBV has electrical properties resembling the parallel plate capacitor with a voltage dependent plate distance d.
The main application for the HBV diode is to generate signals at extremely high frequencies from 100 GHz up to 450 GHz by frequency multiplication
. This is made possible by the highly nonlinear voltage dependence of the capacitance C(V). By feeding the HBV a signal of low frequency f1, higher harmonics f3=3f1, f5=5f1, ... will be generated. Only odd harmonics are generated, since even harmonics are cancelled due to the symmetric nature of the nonlinearity. Also, using this inherent symmetry of the device, it can operate without DC-biasing. This is an advantage compared to the Schottky diode
which has to be biased.
Signals generated at these frequencies (100 GHz - 3 THz) have applications in diverse areas such as radioastronomy, security imaging, biological and medical imaging and high-speed wireless communications.
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
with an anti-symmetric current-voltage relationship and a symmetric capacitance-voltage relationship, as shown in the graph to the right. The device was invented by Erik Kollberg together with Anders Rydberg in 1989 at Chalmers University of Technology
Chalmers University of Technology
Chalmers University of Technology , is a Swedish university located in Gothenburg that focuses on research and education in technology, natural science and architecture.-History:...
.
The inset of the figure shows the circuit schematic symbol of the HBV. From the symbol, one can conclude that the HBV consists of two, back to back, anti-serially connected rectifying diodes (such as Schottky diode
Schottky diode
The Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action...
s for instance). The gap in the middle of the diode symbol represents the inherent capacitance of the device. The electrical characteristics of the HBV are realized by separating two layers of a semiconductor material (A) with a layer of another semiconductor material (B). The band-gap of material (B) should be larger than for material (A). This results in a barrier for the carriers trying to travel through the layers (A)-(B)-(A). The (A) layers are usually n-doped which means that electrons are the majority carriers of this device. At different bias voltages the carriers are redistributed and the distance between the carriers on each side of the barrier (B) is different. As a consequence the HBV has electrical properties resembling the parallel plate capacitor with a voltage dependent plate distance d.
The main application for the HBV diode is to generate signals at extremely high frequencies from 100 GHz up to 450 GHz by frequency multiplication
Frequency multiplier
In electronics, a frequency multiplier is an electronic circuit that generates an output signal whose output frequency is a harmonic of its input frequency. Frequency multipliers consist of a nonlinear circuit that distorts the input signal and consequently generates harmonics of the input signal...
. This is made possible by the highly nonlinear voltage dependence of the capacitance C(V). By feeding the HBV a signal of low frequency f1, higher harmonics f3=3f1, f5=5f1, ... will be generated. Only odd harmonics are generated, since even harmonics are cancelled due to the symmetric nature of the nonlinearity. Also, using this inherent symmetry of the device, it can operate without DC-biasing. This is an advantage compared to the Schottky diode
Schottky diode
The Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action...
which has to be biased.
Signals generated at these frequencies (100 GHz - 3 THz) have applications in diverse areas such as radioastronomy, security imaging, biological and medical imaging and high-speed wireless communications.