ECE 662 Microwave Devices

1
ECE 662Microwave Devices

• Transit-Time Diodes
• February 17, 2005

2
Two-Terminal Negative Resistance Devices
3
Avalanche Transit-Time Devices
4
(No Transcript)
5
Avalanche Transit-Time Devices
6
Avalanche Transit-Time Devices
7
Measured Ionization rates for electrons and holes
vs reciprocal field for Si and GaAs
8
Ref Sze
9
Diode Configurations
10
IMPATT Mode Diodes
11
IMPATT Mode Diodes
12
Injected carriers therefore traverse the length
wD of the drift region During the negative
half-cycle if we choose the transit time to be ½
oscillation period.
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
IMPATT Mode Diodes
17
Double-Drift Region IMPATTs
18
TUNNETT Mode
19
BARrier Injection Transit Time Devices (BARITTs)
20
BARrier Injection Transit Time Devices (BARITTs)
The injected carrier density increases with the
ac voltage. Then the carriers will traverse the
drift region. The injected hole pulse at 90o and
the corresponding induced current which travels
3/4s of a cycle to reach the negative terminal.
Or w/vs ¾ (1/f) Note that for ?/2? ?t??, both
the ac voltage and external current are positive
therefore ac power is dissipated in the device.
Consequently, the BARITT diodes have low power
capabilities and low efficiencies but they also
have low noise (avoiding the avalanche phenomena).
21
TRApped Plasma Avalanche Triggered Transit Time
Devices (TRAPATTs)
22
TRApped Plasma Avalanche Triggered Transit Time
Devices (TRAPATTs)
23
Comparison of Microwave Devices

• An important figure of merit for microwave
  devices is power output as a function of
  oscillation frequency.
• Due to limitations of semiconductor materials,
  the maximum power of a single device at a given
  frequency is limited.
• Two basic limitations
• Critical field, at which avalanche breakdown
  occurs
• Saturation velocity which is the maximum
  attainable velocity in semiconductors

24
Power Output -1

• The maximum voltage that can be applied across a
  semiconductor sample is limited by the break down
  voltage.
• For a uniform avalanche this is Vm EcW where W
  is the depletion layer width
• The maximum current that can be carried by the
  semiconductor is also limited by the avalanche
  breakdown process, because the current in the
  space charge region causes an in crease in the
  electric field.

25
Power Output -2
26
Power Output -3
27
(No Transcript)
28
Solid-State Device Power Output vs Frequencyref
Sze and modifiedby Tian
29
(No Transcript)