GB2368717A

GB2368717A - Gunn diodes

Info

Publication number: GB2368717A
Application number: GB0015887A
Authority: GB
Inventors: Geoffrey Martin Dunn; Michael William Carr
Original assignee: Marconi Applied Technologies Ltd
Current assignee: Teledyne UK Ltd
Priority date: 2000-06-29
Filing date: 2000-06-29
Publication date: 2002-05-08
Also published as: WO2002001652A1; AU2001266177A1; GB0015887D0

Abstract

A Gunn diode comprises a plurality of transit regions 3, 4. Whatever potential is required by the user may be obtained by selecting an appropriate number of transit regions. Hence, power output may be increased compared with conventional devices. The transit regions may be realised in a single device or a plurality of series-connected diodes. The transit regions may be of the same length (as in the drawing) or may be of unequal lengths. The doping in each region may be the same (as indicated by the line 5) or may be different.

Description

23687 1 7

Gunn Diodes This invention relates to Gunn diodes.

The power of a Gunn diode is limited by the amount of potential that can be safely applied before the device becomes vulnerable to breakdown from impact ionization.

5 This is particularly problematic at very high frequencies, in the tens of gigahertz range, where the transit region length must be less than one micron.

In a Gunn diode, the length of the transit region is determined by the amount of time it takes for a charge monopole or dipole to transfer from the cathode to the anode at in approximately 0.75 x 105 may, the optimum operating frequency being approximately 1/T. Thus, GaAs diodes required for high frequency operation, for example 77 GHz or 94 GHz, must be less than one micron in length to operate in a fundamental mode. The size of the diode limits the power available. Only a relatively small potential can be applied before impact ionization causes the device to breakdown. To deal with this, the 5 device may be arranged to operate at half the required frequency to enable power to be extracted in a second harmonic mode. This gives a reduction in efficiency however, but does permit a larger voltage to be applied as the device is longer. Another approach is to use InP instead of GaAs because its higher drift velocities enable longer transit regions to be used. This advantage is offset by the engineering difficulties in using this 20 material compared to GaAs.

The present invention arose from consideration of an improved diode.

According to the invention there is provided a Gunn diode comprising a plurality of transit regions.

By using the invention, by selecting an appropriate number of transit regions whatever 5 potential is required may be obtained. Hence power output may be increased compared to the previously known devices. The invention is particularly applicable to GaAs diodes for the reasons given above, but may be applied to diodes of any material.

The plurality of transit regions may be implemented in a single device or in two or more lo discrete components connected in series. A single device with multiple transit regions however offers a cheap and efficient approach.

A device in accordance with the invention is capable of sustaining charge domains simultaneously in each transit region of the plurality, the charge domains moving 5 coherently with each other. The invention thus permits large power outputs to be achieved, for example, a three or four transit region device may yield power outputs of approximately 300% or 400% respectively greater than a comparable single transit region diode, with little or no change in device efficiency.

20 The transit regions in a device may be substantially identical in length but in other embodiments, multiple transit regions of unequal lengths could be used. This may be advantageous where temperature gradients across the device might cause a non-uniform response. Also, where non-equal length transit regions are used, the device may be resonant at more than one frequency, giving rise to wider applications than conventional

designs. In another embodiment, transit region lengths are non-equal but differ by a relatively small amount which may lead to broadening of the useful frequency range.

The invention is applicable to monopole and dipole modes of operation.

In one embodiment, each transit region of the plurality is similarly doped but in others different doping may be applied to different ones of the transit regions to achieve modified characteristics and performance.

lo Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings, in which: Figure 1 is an explanatory diagram relating to the operation of a Gunn diode with two transit regions; Figure 2 shows the current, electric field and charge density at several different times in

a single transit region device, and Figures 3 and 4 the same parameters for double and triple transit region devices respectively; 20 Figure 5 shows power and efficiency for single and double transit region devices; and Figure 6 shows power and efficiency for three devices at 55 GHz.

With reference to Figure 1, a double transit region Gunn diode in accordance with the 25 invention has a cathode 1 and an anode 2 with two transit regions 3 and 4 between them.

The doping profile of the device is indicated by the unbroken line 5, from which it can be seen that there are highly doped parts 6 and notches 7. The broken line 8 indicates the charge density in the device when operating.

5 With reference to Figure 2, this shows the current at (a), electric field at (b) and charge

density at (c) at several different times in a single transit, conventional device under a 55 GHz potential Vrf ( an imposed radio frequency potential on top of a dc bias) and do potential Vat of 5 V. This may be compared with similar graphs for a double transit region device shown in Figure 3 and a triple transit region device shown in Figure 4.

lo The potential in the latter two devices is increased in proportion to the device size, with V6C=10V and Vrf=4V, and V c=15V and Vrm6V respectively. In each case, the same good antiphase response of the current and potential exists to the 55 GHz potential. In the two multiple transit region devices, the dipoles move across each transit region in phase. Figure 5 shows the device power and efficiency for the single and double transit region devices. The efficiency and frequency responses are almost identical and the power in the double transit region device is almost double that of the single transit region device.

20 Figure 6 shows the power and efficiency of single, double and triple transit region devices. The increase in power achieved in the multiple transit region devices is almost linear whilst the efficiency is substantially the same.

Claims

1. A Gunn diode comprising a plurality of transit regions.

2. A Gunn diode as claimed in claim 1, in which each transit region has a length, and the lengths of the transit regions are substantially equal.

3. A Gunn diode as claimed in claim 1, in which each transit region has a length, and the length of at least one transit region is different from the lengths of the other transit regions.

4. A Gunn diode as claimed in any preceding claim, in which at least one transit region is doped differently from the other transit regions.

5. A Gunn diode arrangement comprising a plurality of Gunn diodes connected in series, each diode having at least one transit region so that the Gunn diode arrangement comprises a plurality of transit regions.

6. A Gunn diode arrangement as claimed in claim 5, in which each transit region has a length, and the lengths of the transit regions are substantially equal.

7. A Gunn diode arrangement as claimed in claim 5, in which each transit region has a length, and the length of at least one transit region is different Tom the lengths of the other transit regions.

8. A Gunn diode arrangement as claimed in any one of claims 5 to 7, in which at least one transit region is doped differently from the other transit regions

9. A Gunn diode, or a Gunn diode arrangement, substantially as hereinbefore described, with reference to, or as illustrated in, the accompanying drawings.

10. A radar system including a Gunn diode or Gunn diode arrangement as claimed in any preceding claim.

11. An automotive radar system including a Gunn diode or Gunn diode arrangement as claimed in any one of claims 1 to 9.

12. A vehicle including automotive radar as claimed in claim 1 1.

13. A method of manufacture of a Gunn diode, including the step of forming a plurality of transit regions.

14. A method of manufacture of a Gunn diode, substantially as hereinbefore described, with reference to, or as illustrated in, the accompanying drawings.