Phase-change material switches with isolated heating elements
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 phase change material (PCM) switch circuit including:
(a) a PCM switch including (1) a PCM region having an input and an output; and (2) a resistive heater adjacent the PCM region and having a first terminal and a second terminal;
(b) a first switch coupled to the first terminal of the resistive heater of the PCM switch and configured to be coupled to a source of state change pulses; and
(c) a second switch coupled to the second terminal of the resistive heater of the PCM switch and configured to be coupled to a ground;
wherein the first and second switches bracket the resistive heater and wherein when the resistive heater is not in an active state heating the PCM region, the first and second switches are set to an open state.
2 . The invention of claim 1 , wherein at least one of the first and second switches is a separate PCM switch.
3 . The invention of claim 1 , wherein the first and second switches and the resistive heater are configured to be coupled to a driver circuit providing an electrical pulse profile.
4 . The invention of claim 3 , further including a driver circuit.
5 . The invention of claim 3 , further including a heater controller configured to provide an electrical pulse profile to the driver circuit.
6 . The invention of claim 1 , 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 PCM region is in an ON state after application of a first electrical pulse profile, and in an OFF state after application of a second electrical pulse profile.
8 . The invention of claim 1 , wherein the PCM switch includes a compensation capacitance coupled between the input and the output of the PCM region in parallel with the PCM region.
9 . A stack of two or more phase change material (PCM) switch circuit having respective PCM regions coupled in series, each PCM switch circuit including:
(a) an associated PCM switch including a resistive heater adjacent a corresponding PCM region, the resistive heater having a first terminal and a second terminal;
(b) a first switch coupled to the first terminal of the resistive heater of the associated PCM switch; and
(c) a second switch coupled to the second terminal of the resistive heater of the associated PCM switch;
wherein the first and second switches of each PCM switch circuit bracket the resistive heater of the associated PCM switch and wherein when the resistive heater of the associated PCM switch is not in an active state heating the PCM region of the associated PCM switch, the first and second switches are set to an open state.
10 . The invention of claim 9 , wherein at least one of the first and second switches of each PCM switch is a PCM switch.
11 . The invention of claim 9 , wherein the first and second switches and the resistive heater are configured to be coupled to a driver circuit providing an electrical pulse profile.
12 . The invention of claim 11 , further including a driver circuit.
13 . The invention of claim 12 , further including a heater controller configured to provide an electrical pulse profile to the driver circuit.
14 . The invention of claim 9 , wherein the first and second switches of each PCM switch are configured to be closed while an electrical pulse profile is to be applied to the corresponding resistive heater, and open while the electrical pulse profile is not to be applied to the corresponding resistive heater.
15 . The invention of claim 9 , wherein the PCM region of each PCM switch is in an ON state after application of a first electrical pulse profile, and in an OFF state after application of a second electrical pulse profile.
16 . The invention of claim 9 , wherein at least one PCM switch includes a compensation capacitance coupled between an input terminal and an output terminal of the at least one PCM switch.
17 . A phase change material (PCM) switch circuit including:
(a) a PCM switch including (1) a PCM region having an input and an output; and (2) a resistive heater adjacent the PCM region and having a first terminal and a second terminal;
(b) a first switch coupled to the first terminal of the resistive heater of the PCM switch;
(c) a second switch coupled to the second terminal of the resistive heater of the PCM switch; and
(d) a circuit for countering variations in resistance of the resistive heater of the PCM switch, the circuit including:
(1) a resistivity sensor for measuring a resistance R H_M of the resistive heater;
(2) a processor, coupled to the resistivity sensor, for calculating scaled current, voltage, and/or 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 values, and for outputting signals indicative of the adjusted electrical pulse profile; and
(3) a heater controller and driver, coupled to the processor and the resistive heater, for applying the adjusted electrical pulse profile to the resistive heater.