Phase-change material switches
Circuits and methods that enable stacking of phase change material (PCM) switches and that accommodate variations in the resistance of the resistive heater(s) of such switches. Stacking is enabled by providing isolation switches for the resistive heater(s) in a PCM switch to reduce parasitic capacitance caused by the proximity of the resistive heater(s) to the PCM region of a PCM switch. Variations in the resistance of the resistive heater(s) of a PCM switch are mitigated or eliminated by sensing the actual resistance of the resistive heater(s) and then determining a suitable adjusted electrical pulse profile for the resistive heater(s) that generates a precise thermal pulse to the PCM region, thereby reliably achieving a desired switch state while extending the life of the resistive heater(s) and the phase-change material.
1. A circuit for countering variations in resistance of a resistive heater of a phase change material (PCM) switch, including:
(a) a resistivity sensor for measuring a resistance R H_M of the resistive heater;
(b) a processor, coupled to the resistivity sensor, for calculating scaled current values as a function of the measured resistance R H_M and a reference resistance R H_REF , for calculating an adjusted electrical pulse profile based on the calculated scaled current values, and for outputting signals indicative of the adjusted electrical pulse profile; and
(c) a heater controller and driver, coupled to the processor and the resistive heater, for applying the adjusted electrical pulse profile to the resistive heater.
2. The invention of claim 1 , wherein the processor includes a lookup table for storing at least the reference resistance R H_REF .
3. The invention of claim 1 , further including a look-up table, coupled to the processor, for storing at least the reference resistance R H_REF .
4. The invention of claim 1 , wherein the resistivity sensor is configured to measure a current through the resistive heater when a known voltage is applied to the resistive heater.
5. The invention of claim 1 , wherein the processor is configured to calculate a scaled current I S using the following formula:
I S =sqrt ( R H_REF /R H_M )* I S_REF
where I S_REF is a reference current amplitude of an electrical pulse for inducing an ON or an OFF state for the PCM switch, and the subscript “S” indicates either an ON state or an OFF state.
6. The invention of claim 1 , wherein the resistive heater includes a first terminal and a second terminal, and further including:
(a) a first switch coupled to the first terminal of the resistive heater; and
(b) a second switch coupled to the second terminal of the resistive heater;
wherein the first and second switches are configured to be closed while an electrical pulse profile is to be applied to the resistive heater, and open while the electrical pulse profile is not to be applied to the resistive heater.
7. The invention of claim 1 , wherein the resistive heater includes a first terminal and a second terminal, and further including:
(a) a first inductor coupled to the first terminal of the resistive heater; and
(b) a second inductor coupled to the second terminal of the resistive heater.
8. A circuit for countering variations in resistance of a resistive heater of a phase change material (PCM) switch, including:
(a) a resistivity sensor for measuring a resistance R H_M of the resistive heater;
(b) a processor, coupled to the resistivity sensor, for calculating scaled voltage values as a function of the measured resistance R H_M and a reference resistance R H_REF , for calculating an adjusted electrical pulse profile based on the calculated scaled voltage values, and for outputting signals indicative of the adjusted electrical pulse profile; and
(c) a heater controller and driver, coupled to the processor and the resistive heater, for applying the adjusted electrical pulse profile to the resistive heater.
9. The invention of claim 8 , wherein the processor includes a lookup table for storing at least the reference resistance R H_REF .
10. The invention of claim 8 , further including a look-up table, coupled to the processor, for storing at least the reference resistance R H_REF .
11. The invention of claim 8 , wherein the resistivity sensor is configured to measure a voltage across the resistive heater when a known current is applied to the resistive heater.
12. The invention of claim 8 , wherein the processor is configured to calculate a scaled voltage V S using the following formula:
I S =sqrt ( R H_REF /R H_M )* I S_REF
where V S_REF is a reference voltage amplitude of an electrical pulse for inducing an ON or an OFF state for the PCM switch, and the subscript “S” indicates either an ON state or an OFF state.
13. The invention of claim 8 , wherein the resistive heater includes a first terminal and a second terminal, and further including:
(a) a first switch coupled to the first terminal of the resistive heater; and
(b) a second switch coupled to the second terminal of the resistive heater;
wherein the first and second switches are configured to be closed while an electrical pulse profile is to be applied to the resistive heater, and open while the electrical pulse profile is not to be applied to the resistive heater.
14. The invention of claim 8 , wherein the resistive heater includes a first terminal and a second terminal, and further including:
(a) a first inductor coupled to the first terminal of the resistive heater; and
(b) a second inductor coupled to the second terminal of the resistive heater.
15. A circuit for countering variations in resistance of a resistive heater of a phase change material (PCM) switch, including:
(a) a resistivity sensor for measuring a resistance R H_M of the resistive heater;
(b) a processor, coupled to the resistivity sensor, for calculating scaled time values as a function of the measured resistance R H_M and a reference resistance R H_REF , for calculating an adjusted electrical pulse profile based on the calculated scaled time values, and for outputting signals indicative of the adjusted electrical pulse profile; and
(c) a heater controller and driver, coupled to the processor and the resistive heater, for applying the adjusted electrical pulse profile to the resistive heater.
16. The invention of claim 15 , further including a look-up table, coupled to the processor, for storing at least the reference resistance R H_REF .
17. The invention of claim 15 , wherein the processor is configured to calculate a scaled time T S_I using the following formula:
T S_I =( R H_REF /R H_M )* T S_REF
where T S_REF is a reference time duration of an electrical pulse for inducing an ON or an OFF state for the PCM switch, and the subscript “S” indicates either an ON state or an OFF state.
18. The invention of claim 15 , wherein the processor is configured to calculate a scaled time T S_V using the following formula:
T S_V =( R H_M /R H_REF )* T S_REF
where T S_REF is a reference time duration of an electrical pulse for inducing an ON or an OFF state for the PCM switch, and the subscript “S” indicates either an ON state or an OFF state.
19. The invention of claim 15 , wherein the resistive heater includes a first terminal and a second terminal, and further including:
(a) a first switch coupled to the first terminal of the resistive heater; and
(b) a second switch coupled to the second terminal of the resistive heater;
wherein the first and second switches are configured to be closed while an electrical pulse profile is to be applied to the resistive heater, and open while the electrical pulse profile is not to be applied to the resistive heater.
20. The invention of claim 15 , wherein the resistive heater includes a first terminal and a second terminal, and further including:
(a) a first inductor coupled to the first terminal of the resistive heater; and
(b) a second inductor coupled to the second terminal of the resistive heater.