What is a Baritt diode?
The Baritt diode is a type of transit time device, it is a microwave frequency signal generation device that covers all the parameters such as capacitance effect, inductance effect, and most importantly transit time or the time taken between signal injection to input and taken out from output.
Avalanche transit time devices
The applications like microwave generation, special devices are needed to operate at high frequencies. But operating on microwave frequencies is not a simple thing to do, we need to satisfy some more parameters such as capacitance effect, inductance effect, and transit time of the device.
These parameters did not overcome with a common diode or device, we need a special device for these operations, and here is the importance of avalanche transit time device.
Three types of transit time diodes
- Trapatt diode
- Impatt diode
- Baritt diode
These are the examples of avalanche transit-time diodes, each of the diodes are used in microwave generation applications, but the theory behind the operations of each of these diodes is different. In this article, we discuss the Baritt diode.
Full form of Baritt diode
Barrier Injection Transit Time diode is the full form of Baritt diode
symbol of Baritt diode
Baritt diode doesn’t have a special symbolic representation, most of the circuits the Baritt diodes are represented with the conventional diode symbol.
the Construction of Baritt diode
Construction-wise Baritt diode is much similar to the Impatt diode, on both ends of the structure p-type is placed and at the inner portion, two n-type semiconductors are placed small n-type and the n-type wider drift region.
Both the p-type portions at the ends are made with metal material and both n-type are made with a semiconductor material, all of these form an M-N-M structural arrangement.
The whole Baritt diode arrangement reminds us of the two diodes connected back-to-back, this is why we divide the Baritt diode into three portions, first p-type is the emitter, then the small n-type portion as the base, and the last p-type portion as the collector.
working principle of Baritt diode
The operation of the Baritt diode will have happened only on the base to emitter region because at the drift region or collector there are free-of-charge carriers.
The energy band diagram shows, when a voltage is applied is responsible for the microwave generation, we already know Baritt diode is a back-to-back pair of the diode.
The microwave generation of the Baritt diode is occurred by two operations, thermionic emission or injection and difference of minority carriers across the forward-biased barrier.
The figure shows the graphical representation of the working operation of the Baritt diode.
In the figure we can see three graphs, the first graph shows the initial voltage injected into the device, the punch-through effect occurs and the signal is in-phase with RF voltage waveform.
Then the initial signal results from an increase in current, but the current wave is just like a strike with regular intervals, as in the second graph.
The last graph represents the terminal current and positive and negative resistance values, the Baritt diode has higher positive resistance than the Impatt diode, so the losses are higher at it.
The width of the current pulse is set by the device transit time value, and also the power of the signal is based on the frequency value of the signal.
Thermionic emission or injection
The thermionic emission or thermionic injection is the main property behind the operation of the Baritt diode the property thermionic emission is the operation behind the vacuum tubes, the working is very simple, the transportation of the electron from one electrode to another electrode is by heating the main electrode and the heat will transfer the electrons to the second location.
This is why vacuum tubes are known as the voltage controlling device, but in a Baritt diode the operation is slightly different, here we don’t have an electrode for electron transfer, but the p-type substrate with metallic material is used to start the thermionic emission.
The operation of the Baritt diode will start with the injection of higher voltage into the device, the high voltage difference produces tension on the diode, and the barrier experience a high current strike with high negative resistance.
The high negative resistance value produces losses in the form of rising heat on the device.
Features of Baritt diode
- Operating frequency = 4GHz to 8GHz
- Operation principle = Thermionic emission or injection
- Output power = few milli-watts
- Efficiency = 5% at low frequency and 20% at high frequency
- Noise figure = 15db low NF
Critical voltage or initial voltage formula
V = q NL2/ 2ES
N= Doping concentration
L= Semiconductor thickness
ES= Semiconductor dielectric permittivity
The critical voltage is the value needed for the Baritt diode to kick start the process, the high voltage outbreak results from the thermionic injection toward the depletion layer which is on a reverse bias condition.
But the critical voltage will be set with three conditions, doping concentration at the silicon substrate of drift region and thickness of the semiconductor material, these conditions are directly proportional.
But the permittivity offered by the semiconductor is inversely proportional, so this value sets the barrier tension.
Advantages & disadvantages of Baritt diode
- Less noise operation due to thermionic emission
- Low noise figure suitable for amplifier circuits
- Low efficiency
- Narrow bandwidth
- Low power output
Baritt diode uses
- Used in microwave generations
- Used in burglar alarm applications
- Used in RF oscillator
- Used as the small-signal amplifier
- Mixer circuit