Patent Description:
The technical requirements for radio frequency (RF) applications using high frequencies, such as radar sensing and mobile communication according to the <NUM> standard, are increasing. In particular, switches having improved characteristics compared to state-of-the-art CMOS switches will be required to meet future demands. Phase change switches are considered as promising candidates for switching RF signals. Such phase change switches use a phase change material (PCM) which typically exhibits a higher electric conductivity in a crystalline phase state than in an amorphous phase state. By changing the phase state of the phase change material, a switching device including such a material may be switched on or off.

For example, to change the phase state from amorphous to crystalline, typically a heater is employed heating the phase change material causing crystallization. This switching on is also referred to as a set operation of the switching device. In this set operation, the heater is actuated in such a way that the temperature of the phase change material is above its crystallization temperature, typically about <NUM>, but below the melt temperature of typically in a range of <NUM> to <NUM>, for example. The length of the heating pulse caused by the heater is chosen such that any amorphous region present in the PCM can regrow into the crystalline phase state.

When switching off the switching device, also referred to as reset operation, the heater is actuated in such a way that the temperature of the PCM is raised above the melt temperature (for example above about <NUM> to <NUM>), followed by rapid cooldown which freezes the phase change material into an amorphous state.

Besides that intended switching, also an unintended switching of such a switch device may happen, for example due to overvoltage conditions. Such overvoltage conditions may for example be caused by an electrostatic discharge (ESD) event.

A high voltage discharge (e.g. in the kilovolt range) in such an electrostatic discharge event may cause heating of the phase change material and thus unintended switching of the state or setting of the switch to a mixed state where part of the PCM is crystalline and part amorphous. While usually electric circuits are protected against ESD events by dedicated ESD protection circuitry, this is difficult to implement for radio frequency applications, as providing such ESD protection circuitry coupled to the phase change switch may adversely affect the radio frequency behavior of the switch.

A related problem exists when starting up a system including phase change switches. In such cases, the state of the phase change switches may be unknown, and the phase change switches may be needed to be brought to a desired state by applying corresponding heating, as described above. This takes time, causes heat in the system, consumes current and counts against a number of switching cycles defining a lifetime of the switch device.

<NPL> discloses a pahse change memory device using phase change switches as memory cells.

<CIT> discloses another phase change switch device.

<CIT> discloses a semiconductor switch where an initial state is stored in a memory, and the semiconductor switch is set to the state stored in the memory.

A device as defined in claim <NUM> and a method as defined in claim <NUM> are provided. The dependent claims define further embodiments.

According to an embodiment, a device is provided, comprising:.

According to another embodiment, a method is provided, comprising:.

The above summary is merely intended to give a brief overview over some embodiments and is not to be construed as limiting in any way.

In the following, various embodiments will be described in detail referring to the attached drawings. The embodiments described hereinafter are to be taken as examples only and are not to be construed as limiting. For example, while in embodiments specific arrangements or components are provided, in other embodiments other configurations may be used.

Besides features (for example components, elements, acts, events or the like) explicitly shown and described, in other embodiments additional features may be provided, for example features used in conventional switch devices using phase change materials. For example, embodiments described herein relate to monitoring a state of a switch, which is based on a phase change material, and other components and features, like control circuitry for controlling a heater, radio frequency (RF) circuitry using the switch device and the like may be implemented in a conventional manner. Such additional components may be integrated with the described switch devices on the same substrate, but may also be provided separately for example on one or more separate chip dies, which in some implementations then may be combined with a switch device in a common package. Also, structural implementations, like providing phase change material on a substrate like a silicon substrate to implement a phase change switch, providing phase change material in a trench in a silicon substrate and the like may be performed in any conventional manner.

A switch based on a phase change material (PCM) will be referred to as a phase change switch or short PCM switch herein. As explained in the introductory portion, such phase change switches may be set to a crystalline phase state or an amorphous phase estate, thus changing the resistance of the phase change material and therefore of the switch by several orders of magnitude. An illustrative example is shown in <FIG> illustrates the resistance of an example phase change material over temperature. In an amorphous phase state, the example resistance is high, above <NUM><NUM> Ohm. By heating as illustrated by a curve portion <NUM> to about <NUM>, the phase change material may be brought to a crystalline phase, in this case to a face-centered cubic (fcc) crystalline phase, which, as illustrated by a curve part <NUM>, is preserved when cooling. The resistance in this case is then below <NUM><NUM> Ohm, i.e. more than three orders of magnitude lower. By using appropiate dimensions (length and width) of the phase change material for a PCM switch, an on-resistance of the switch for example in a range of <NUM> to <NUM> Ohm may be achieved.

Implementation details described with respect to one of the embodiments are also applicable to other embodiments. For example, with respect to <FIG> possible phase change materials and materials for a heater are described, and these may also be used in other embodiments described herein and will therefore not be described repeatedly.

Turning now to the figures, <FIG> illustrates a switch device according to an embodiment.

<FIG> comprises a phase change switch <NUM> including a phase change material <NUM> and a heater <NUM>. Phase change material <NUM> is coupled between a first radio frequency terminal RF1 and a second terminal radio frequency terminal RF2, to selectively couple radio frequency terminal RF1 to radio frequency terminal RF2. In other embodiments, none-radio-frequency signals may be used. Radio frequency, in this respect, refers to signal having a frequency having at least <NUM>, for example above <NUM>, for example in the gigahertz (Ghz) range. Phase change switch <NUM> may for example be used in antenna tuning applications, to selectively couple capacitances or inductances to an antenna.

By being coupled between RF terminals RF1 and RF2, radio frequency switch <NUM> is prone to experiencing overvoltages for example due to electrostatic discharges (ESD) at an antenna as mentioned above or otherwise occuring at RF terminal RF1 or RF2. Moreover, as explained in the introductory portion, protecting phase change switch <NUM> by conventional ESD protection circuitry may negatively affect the radio frequency properties of switch device <NUM> and is therefore not desirable in some applications.

An example for a usable phase change material <NUM> is germanium telluride. Heater <NUM> may be made of materials like polycrystalline silicon or tungsten. Heater <NUM> is controlled by a controller <NUM> to switch phase change material <NUM> between the crystalline phase state and the amorphous phase state, as explained above with respect to <FIG>. This may be done in response to a control signal ctrl provided to controller <NUM>. This control may be performed in any conventional manner, as already mentioned above.

In addition to this conventional control, controller <NUM> is configured to monitor the state of phase change material <NUM> and therefore of phase change switch <NUM>. For this monitoring, a voltage may be applied to phase change material <NUM> using connections 16A, 16B, and a corresponding current may be measured. In other embodiments, a predefined current may be applied via connections 16A, 16B, and the voltage drop over phase change material <NUM> may be measured. The voltage or current applied and the voltage or current measured may be DC voltages and currents, applied and measured via radio frequency decoupling elements 12A, 12B. Radio frequency decoupling elements 12A, 12B may for example be inductors, which exhibit a high impedance for RF signals, but a low impedance for DC signals, or high ohmic resistors. In this way, the monitoring by controller <NUM> in some embodiments does not significantly affect the radio frequency operation of phase change switch <NUM>, i.e. the selective coupling of radio frequency terminals RF1 and RF2. While DC voltages and currents are used in the above example, in other embodiments also AC currents with a frequency lower than a frequency of radio frequency signals phase change switch <NUM> is designed for.

For example, if phase change switch <NUM> is designed to switch RF signals in the GHz range, for monitoring the state measurement signals (as the currents and voltages above) having a frequency at least a factor <NUM> or a factor <NUM> lower, for example <NUM> or lower, may be used. Such a frequency different enables a design of radio frequency decoupling elements 12A, 12B that block the radio frequency signals, but let the measurement signals pass, for example as low pass filters (for which inductors are a simple example) having a cut-off frequency between the frequency of the RF signals and the frequency of the measurement signals.

By this monitoring, the state (set or reset) of phase change switch <NUM> may be measured. For example, phase change switch <NUM> may be designed to have an on resistance of <NUM> Ohm and an off resistance between <NUM> to <NUM> Kiloohm. By above measurement, the resistance (on, off or even intermediate) may be determined by controller <NUM>.

A target state of phase change switch <NUM> is stored in a memory <NUM> coupled to controller <NUM>. The target state is the state (set or reset) the phase change switch <NUM> is intended to be in, for example as determined by control signal ctrl.

Memory <NUM> may be any kind of suitable memory. In embodiments, memory <NUM> is a non-volatile memory. For example, memory <NUM> may include a flash memory. In some implementations, memory <NUM> may include a phase change memory. A phase change memory is a memory essentially corresponds to a phase change switch, where the state of the phase change material (set or reset) corresponds to a value (for example <NUM> or <NUM>) stored in the memory. In case of implementation as a phase change memory, memory <NUM> may be manufactured together with phase change switch <NUM> concurrently, i.e. during the same processing stages. It should be noted that phase change memories in many implementations do not require a separate heater, but a direct heating e.g. using a heating current through the phase change material may also be used.

Controller <NUM> may compare the state of phase change switch <NUM> as measured with the target state stored in memory <NUM>. In case of a deviation (i.e. state of phase change switch <NUM> does not correspond to the target state), controller <NUM> may control heater <NUM> to set or reset phase change switch <NUM> to the target state.

In some embodiments, the monitoring of the state of phase change switch <NUM> by controller <NUM> may be continuous. In such a situation, controller <NUM> may for example update the target state in memory <NUM> each time control signal ctrl indicates a change of the target state.

A first application example of this monitoring, in particular in case of continuous monitoring, is protection against undesired state changes of phase change switch <NUM>. Such undesired changes, as already mentioned above, may be due to electrostatic discharges at terminals RF1 or RF2, which lead to heating of phase change material <NUM> and may therefore change the phase state of phase change switch <NUM>. Such an inadvertent state change may then be detected by controller <NUM>, and upon detection phase change switch <NUM> may be brought to the target state indicated by memory <NUM>.

Additionally or alternatively, memory <NUM> may store a target state for starting up of a device including phase change switch <NUM>. Usually, at such a startup, the state of phase change switches used is undefined, and all switches need to be set or reset, which consumes energy and causes heating. In embodiments, controller <NUM> determines if the state of phase change switch <NUM> at startup corresponds to the target state stored in memory <NUM>, and only controls heater to bring phase change switch <NUM> to the target state in case of a deviation, i.e. if phase change switch <NUM> is not already in the target state. In this way, switching is only necessary if the state of phase change switch <NUM> differs from the target state. This may result in lower power consumption and also in a lower cycling rate of the switch (less switching events), which may extend the lifetime of phase change switch <NUM> in some embodiments.

In this case, no continuous monitoring needs to be performed, but the state of phase change switch <NUM> may be monitored by controller <NUM> only at startup.

It should be noted that the two approaches may be combined, i.e. memory <NUM> may store both a target state for startup and a target state during normal operation (the latter based for example on control signal ctrl), and the monitoring may be performed both at startup and continuously during normal operation. Instead of a continuous monitoring, also a monitoring in regular or irregular intervals is possible.

It should be noted that while phase change switch <NUM> may be prone to electrostatic discharge events as described above, even if memory <NUM> is implemented using a phase change material, it may be protected from electrostatic discharge event together with other parts of the device (for example controller <NUM>) by conventional ESD protection circuitry, as memory <NUM> does not need to switch radio frequency signals and therefore an influence of the ESD protection circuitry on any RF performance is not a consideration here, in contrast to phase change switch <NUM>.

<FIG> illustrates a device according to a further embodiment. In order to avoid repetitions, when describing the device of <FIG>, reference will be made to the description of <FIG> for similar parts.

The embodiment of <FIG> comprises two phase change switches 20A, 20B provided in a single pole double throw (SPDT) configurations between radio frequency terminals RF1, RF2, RF3, as shown. Single pole double throw means that for example RF terminal RF2 may be selectively coupled to RF terminal RF1, RF terminal RF3 or both RF terminals RF1 and RF3, by operating phase change switches 20A and 20B accordingly. Such a configuration is for example sometimes used in antenna tuning applications or other RF applications. The SPDT configuration is only an example, and other switch configurations like general single pole multi throw (multi being double in the example of <FIG>, but may also be triple etc.), single pole single throw (SPST), essentially shown in <FIG>, double pole double throw (DPDT) etc. may also be used.

Each phase change switch 20A, 20B includes a phase change material and a heater, as explained for phase change switch <NUM> of <FIG>, which is controlled by a controller (not fully shown in <FIG>, see controller <NUM> of <FIG>) to set or reset the respective phase change switch 20A, 20B.

For phase change switch 20A, a phase change memory 23A is provided storing a target state for phase change switch 20A, and for phase change switch 20B a phase change memory 23B is provided storing a target state for phase change switch 20B. This storing of a target state may be performed as explained for memory <NUM> of <FIG>.

A comparator circuit 22A, which may be part of a controller like controller <NUM>, is coupled to phase change switch 20A via decoupling inductors 21A, 21B, which are an example for decoupling elements 12A, 12B. Comparator circuit 22A provides one of a DC voltage or a DC current to phase change switch 20A via inductors 21A, 21B and measures the respective other one of DC voltage and DC current, as already explained for controller <NUM> in <FIG>. Likewise, comparator circuit 22A provides one of a DC voltage or a DC current to phase change memory 23A and measures the other one of a DC voltage or a DC current, to read out phase change memory 23A. Comparator circuit 22A then compares the two measurements, which corresponds to comparing the phase change state of phase change switch 20A with the target state stored in phase change memory 23A, and provides the result for example to other parts of a controller like controller <NUM> of <FIG>. As explained for <FIG>, the controller may control a heater of phase change switch 20A to set phase change switch 20A to the target state in case the state is different from the target state. As explained with respect to <FIG>, this may be done at startup, continuously or discontinuously during normal operation, or both.

In a similar manner, for phase change switch 20B a comparator circuit 22B, a phase change memory 23B and inductors 21C, 21D coupled between comparator circuit 22B and phase change switch 20B are provided, which serve the same function as comparator circuit 22A, phase change memory 23A, and inductors 21A and 21B for phase change switch 20A, and will therefore not be described again in detail.

While two phase change switches 20A, 20B are shown in <FIG>, also more phase changes switches may be used, with a correspondingly higher number of comparator circuits and, phase change memories and inductors. Instead of phase change memories 23A, 23B, as explained for memory <NUM> of <FIG>, other types of memories may be provided. For example, a flash memory may be provided which stores target states for both phase change switch 20A and a phase change switch 20B.

Inductors 21A to 21D are dimensioned such that they, for radio frequencies the device is intended to be used for, have a sufficiently high impedance such that the radio frequency switching operation of phase change switches 21A, 21B is essentially not influenced by the monitoring. It should be noted that in embodiments where monitoring is only performed at startup, RF decoupling elements 12A, 12B and corresponding inductors 21A to 21D may be omitted. The same applies to devices where for example a monitoring is performed discontinuously only during times where the RF switching operation of phase change switches 20A, 20B is not used, for example where no radio frequency signals are present or are processed.

<FIG> illustrates a method according to some embodiments. The method of <FIG> may be implemented using the devices shown in <FIG> and, in order to avoid repetitions, will be explained referring to <FIG>. However, it is to be understood that the method of <FIG> may also be implemented using other devices.

At <NUM>, the method of <FIG> comprises determining the state of a phase change switch. This determining may be done as explained with reference to <FIG>, i.e. by applying one of a DC voltage or a DC current to a phase change material of the phase change switch and measuring the other one of DC voltage and DC current.

At <NUM>, the method comprises comparing the determined state to a stored target state, for example stored in memory <NUM> of <FIG> or phase change memory 23A or 23B of <FIG>. If the states are equal, in case of continuous monitoring the determining at <NUM> and the comparing at <NUM> are performed continuously. If, for example if the method is performed only at startup, if the states are equal, the method ends, and normal operation follows.

If the states are unequal, at <NUM> the method comprises changing the state of the phase change switch to the target state, by controlling a heater like heater <NUM> of <FIG> accordingly. After <NUM>, in case of continuous monitoring the determining at <NUM> and the comparing at <NUM> are repeated. Otherwise, for example if the method is performed only at startup, after <NUM> the method terminates, and normal operation follows.

<FIG> is a flowchart illustrating a method for manufacturing a switch device. The method of <FIG> may for example be used to manufacture the switch devices of <FIG>, but by itself is not a method of an embodiment claimed herein. The method of <FIG>, however, may also be used to manufacture other switch devices, including switch devices which do not use a monitoring of the state of a phase change switch as explained above with reference to <FIG>.

At <NUM>, the method comprises forming a phase change switch. This forming may include depositing a phase change material, depositing a heater material and electrically contacting the phase change material and the heater material.

Claim 1:
A device, comprising:
a phase change switch (<NUM>; 20A, 20B) including a phase change material (<NUM>) and a heater (<NUM>),
a memory (<NUM>; 23A, 23B) configured to store a target state for the phase change switch, and
a controller (<NUM>; 22A, 22B) configured to determine a state of the phase change switch, to compare the determined state with the target state, and to control the heater (<NUM>) of the phase change switch (<NUM>) to change the state of the phase change switch to the target state if the state of the phase change switch does not correspond the target state.