Radio frequency transistor amplifiers having engineered instrinsic capacitances for improved performance
Gallium nitride based RF transistor amplifiers include a semiconductor structure having a gallium nitride based channel layer and a gallium nitride based barrier layer thereon, and are configured to operate at a specific direct current drain-to-source bias voltage. These amplifiers are configured to have a normalized drain-to-gate capacitance at the direct current drain-to-source bias voltage, and to have a second normalized drain-to-gate capacitance at two-thirds the direct current drain-to-source bias voltage, where the second normalized drain-to-gate capacitance is less than twice the first normalized drain-to-gate capacitance.
1. A radio frequency (“RF”) transistor amplifier, comprising:
a semiconductor structure that includes a gallium nitride based channel layer and a gallium nitride based barrier layer that has a higher bandgap than the gallium nitride based channel layer on the gallium nitride based channel layer;
a source contact on the gallium nitride based barrier layer;
a drain contact on the gallium nitride based barrier layer; and
a gate contact on the gallium nitride based barrier layer between the source contact and the drain contact,
wherein the RF transistor amplifier is configured to operate at a first direct current drain-to-source bias voltage,
wherein the RF transistor amplifier is configured to have a normalized drain-to-source capacitance that maintains at least 85% symmetry for a range of drain-to-source voltages about the first direct current drain-to-source bias voltage that is equal to 50% of the first direct current drain-to-source bias voltage, and
wherein a normalized drain-to-gate capacitance response of the RF transistor amplifier varies by less than a factor of four for all values of the drain-to-source voltage that are between one half the first direct current drain-to-source bias voltage and twice the first direct current drain-to-source bias voltage.
2. The RF transistor amplifier of claim 1 , wherein a normalized drain-to-gate capacitance response of the RF transistor amplifier varies by less than a factor of three for all values of the drain-to-source voltage that are between one half the first direct current drain-to-source bias voltage and twice the first direct current drain-to-source bias voltage.
3. The RF transistor amplifier of claim 1 , wherein a normalized drain-to-gate capacitance response of the RF transistor amplifier varies by less than a factor of two for all values of the drain-to-source voltage that are between two-thirds the first direct current drain-to-source bias voltage and twice the first direct current drain-to-source bias voltage.
4. The RF transistor amplifier of claim 3 , wherein the RF transistor amplifier is configured to have a first normalized drain-to-gate capacitance at the first direct current drain-to-source bias voltage, and to have a second normalized drain-to-gate capacitance at two-thirds the first direct current drain-to-source bias voltage, and
wherein the second normalized drain-to-gate capacitance is less than twice the first normalized drain-to-gate capacitance.
5. The RF transistor amplifier of claim 1 , wherein the RF transistor amplifier is configured to have a normalized drain-to-source capacitance response that maintains at least 90% symmetry for a range of drain-to-source voltage values about the first direct current drain-to-source bias voltage that is equal to 50% of the first direct current drain-to-source bias voltage.
6. The RF transistor amplifier of claim 1 , wherein the RF transistor amplifier is configured so that a normalized drain-to-gate capacitance response varies by less than 100% for drain-to-source voltages in a range from the first direct current drain-to-source bias voltage to 20 volts below the first direct current drain-to-source bias voltage.
7. The RF transistor amplifier of claim 1 , wherein values of the normalized drain-to-gate capacitance are less than 4×10 −15 farads per watt for all drain-to-source voltage values greater than 32 volts.
8. The RF transistor amplifier of claim 1 , wherein values of the normalized drain-to-gate capacitance are less than 5×10 −15 farads per watt for all drain-to-source voltage values greater than 24 volts.
9. The RF transistor amplifier of claim 1 , wherein values of the normalized drain-to-gate capacitance are less than 6×10 −15 farads per watt for all drain-to-source voltage values greater than 24 volts.
10. The RF transistor amplifier of claim 1 , wherein the first direct current drain-to-source bias voltage is between 48 volts and 55 volts, and wherein values of the normalized drain-to-gate capacitance are less than 5×10 −15 farads per watt for all drain-to-source voltage values greater than 30 volts.
11. The RF transistor amplifier of claim 1 , wherein the first direct current drain-to-source bias voltage is 48 volts, and wherein the RF transistor amplifier is configured to have a normalized drain-to-source capacitance that maintains at least 85% symmetry over a range of drain-to-source voltages from 36 volts to 60 volts.
12. The RF transistor amplifier of claim 1 , wherein the first direct current drain-to-source bias voltage is 48 volts, and wherein the RF transistor amplifier is configured to have a normalized drain-to-source capacitance that maintains at least 70% symmetry over a range of drain-to-source voltages from 24 volts to 72 volts.
13. The RF transistor amplifier of claim 1 , wherein the RF transistor amplifier is configured to have a first normalized drain-to-gate capacitance at the first direct current drain-to-source bias voltage, and to have a second normalized drain-to-gate capacitance at two-thirds the first direct current drain-to-source bias voltage, and
wherein the second normalized drain-to-gate capacitance is less than twice the first normalized drain-to-gate capacitance.
14. A radio frequency (“RF”) transistor amplifier, comprising:
a semiconductor structure that includes a gallium nitride based channel layer and a gallium nitride based barrier layer that has a higher bandgap than the gallium nitride based channel layer on the gallium nitride based channel layer;
a source contact on the gallium nitride based barrier layer;
a drain contact on the gallium nitride based barrier layer; and
a gate contact on the gallium nitride based barrier layer between the source contact and the drain contact,
wherein the RF transistor amplifier is configured to operate at a first direct current drain-to-source bias voltage,
wherein the RF transistor amplifier is configured to have a normalized drain-to-source capacitance that maintains at least 85% symmetry for a range of drain-to-source voltages about the first direct current drain-to-source bias voltage that is equal to 50% of the first direct current drain-to-source bias voltage, and
wherein the RF transistor amplifier is configured so that a normalized drain-to-gate capacitance response varies by less than 100% for drain-to-source voltages in a range from the first direct current drain-to-source bias voltage to 20 volts below the first direct current drain-to-source bias voltage.
15. The RF transistor amplifier of claim 14 , wherein the first direct current drain-to-source bias voltage is between 48 volts and 55 volts, and wherein values of the normalized drain-to-gate capacitance are less than 6×10 −15 farads per watt for all drain-to-source voltage values greater than 24 volts.
16. The RF transistor amplifier of claim 14 , wherein the first direct current drain-to-source bias voltage is between 48 volts and 55 volts, and wherein the normalized drain-to-gate capacitance response varies by less than a factor of three for all values of the drain-to-source voltage that are between one half the first direct current drain-to-source bias voltage and twice the first direct current drain-to-source bias voltage.
17. The RF transistor amplifier of claim 16 , wherein the RF transistor amplifier is configured to have a normalized drain-to-source capacitance response that maintains at least 90% symmetry for a range of drain-to-source voltage values about the first direct current drain-to-source bias voltage that is equal to 50% of the first direct current drain-to-source bias voltage.