Patent Description:
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 by causing crystallization is also referred to as a set operation. In the 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 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 portion 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 a comparatively rapid cooldown which freezes the phase change material or at least a portion thereof into an amorphous state.

Suitable phase change materials used for such phase change switches include germanium telluride (GeTe) or germanium-antimony-tellurium (GeSbTe, usually referred to as GST), and heaters may be made of a material like polycrystalline silicon or tungsten.

PCM switch devices promise excellent radio frequency performance in comparison to state of the art CMOS RF switches. In particular, the main figure of merit, the product of on-resistance and off capacitance, is reduced significantly from around <NUM> fsec for CMOS RF switches to values below <NUM> fsec for PCM switch devices.

In particular, a low off capacitance is desirable in applications like antenna tuning, as resonant modes of tuning networks including such switches may adversely influence the antenna properties at a high operating frequency.

For example, when for tuning purposes such a PCM switch is coupled in series to an inductor having an inductance L, the off state capacitance COFF of the switch creates a series resonance at a frequency <MAT>. This resonance frequency must be shifted to a value outside the operating frequency range of the respective system, for example radio frequency antenna, by either minimizing the inductance value L or minimizing Coff. The latter option is preferred, as it offers a higher degree of freedom in choosing the tuning elements, in particular inductances thereof, of a system.

<CIT> discloses a phase change switch device with a conventional heater and tuning transistors. Such a device is also disclosed in <CIT>, where a heat valve is provided below the heater and a so-called nugget is placed between the heater and a phase change material for electrical isolation and thermal coupling.

<CIT> discloses a phase change memory with a heater.

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

According an embodiment, a phase change material switch device is provided, comprising:.

According to another embodiment, a method of operating a phase change material switch device is provided, the phase change material switch device comprising a phase change material and a heater device thermally coupled to the phase change material, the method comprising:
switching a state of the phase change switch device by setting the heater device to a first state with a first electrical resistance and providing current through the heater device for heating the phase change material, and setting the heater device to a second state with a second electrical resistance higher than the first electrical resistance outside heating phases of the heater device.

The above summary is merely intended as a brief overview over some embodiments and is not to be construed as limiting in any way, as other embodiments may include different features from the ones listed above.

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.

Implementation details described with respect to one of the embodiments are also applicable to other embodiments. Features from different embodiments may be combined to form further embodiments.

Variations and modifications described for one of the embodiments may also be applied to other embodiments and will therefore not be described repeatedly.

In the Figures, like elements are designated with the same reference numerals. Such elements will not be described repeatedly in each Figure to avoid repetitions. Any directional terminology used when referring to the drawings (e.g. up, down, left, right) is merely for indicating elements and directions in the drawings and is not intended to imply a directional orientation of the actually implemented devices.

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 equalization devices in phase change material (PCM) switch devices, and other components and features, like spatial arrangement of heaters and phase change material, radio frequency (RF) circuitry using the switch device and the like may be implemented in a conventional manner. Such RF circuitry 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, manufacturing implementations like providing phase change material on a substrate like a silicon substrate to implement a PCM switch device or in a part thereof like a trench for manufacturing the switch device 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 (PCS) or 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 change, thus changing the resistance of the phase change material and therefore of the switch by several orders of magnitude. In this way, for example an on-resistance of a switch in a range of <NUM> to <NUM>Ω may be achieved, whereas an off-resistance may be several orders of magnitude higher, for example at least in the Kiloohm range.

PCM switch devices discussed herein may be manufactured for example in layer deposition and pattering processes similar to those used in semiconductor device manufacturing, by depositing or modifying layers on a substrate. In some embodiments discussed herein, cross-sectional views and top views are illustrated. A cross-sectional view essentially corresponds to a cross section through the substrate, whereas a top view is a view in a direction towards a surface of the substrate.

While phase change switch devices in the embodiment below are shown with a configuration where a heater is provided below a phase change material, in other embodiments the heater may be provided above the phase change material. Furthermore, currents through the phase change material and through the heater may run in the same direction or in different, for example perpendicular directions. Therefore, the specific configurations shown are not to be construed as limiting in any way.

Turning now to the Figures, <FIG> illustrates a phase change material switch device, PCM switch device <NUM> according to an embodiment. PCM switch device <NUM> includes a phase change material <NUM>, contacted by electrodes 13A, 13B. A heater <NUM> is placed adjacent to phase change material <NUM>, electrically isolated but thermally coupled to phase change material <NUM>. By heating phase change material <NUM> using heater <NUM>, as in conventional PCM switch devices, phase change material <NUM> may be selectively set to a crystalline, electrically conducting state or to an amorphous, electrically isolating state. It should be noted that in the amorphous state phase change material <NUM> need not become fully amorphous, but some crystalline portions may remain for example in the vicinity of electrodes 13A, 13B, as long as the phase change material in the amorphous state provides an electrical isolation between electrodes 13A and 13B. Phase change material <NUM> may be any suitable phase change material described in the introductory portion.

Heater <NUM> is controlled and supplied with power by a heater feed/control entity <NUM>. Heater <NUM>, controlled by entity <NUM>, may at least be in a first state or in a second state, which does not exclude further states being possible. In a first state, the heater has a first electrical resistance suitable for heating. This state, in other words, is used for heating phase change material <NUM> to perform a set or a reset operation as explained in the introductory portion, by feeding current through the heater. The first electrical resistance in the first state is such that heat is generated by dissipation of electrical power.

In the second state, heater <NUM> is configured to have a second electrical resistance higher than the first electrical resistance in the first state. For example, the first electrical resistance may be 500Ω or less , 100Ω or less or 50Ω or less and the second electrical resistance may be at least <NUM> times higher than the first electrical resistance, for example at least <NUM> times higher or about <NUM> times higher, for example 10kΩ or higher. Higher resistances like about 500Ω may for example occur in a hot state of the heater, where the heating increases the resistance. In some cases, in the second state the heater may be essentially electrically insulating. The second state may be used outside heating phases of the heater device, for example generally outside the heating phases or at least in a switched-off state of the PCM switch device <NUM>. In some embodiments, this may reduce a parasitic capacitance between electrodes 13A, 13B and heater <NUM> in an off state of PCM switch device <NUM>. This will now be explained in more detail referring to <FIG> (including subfigures 2A and 2B), <NUM> and <NUM> (including Subfigures 4A and 4B).

<FIG> shows a top view of a PCM switch device according to a comparative example, and <FIG> shows a cross-section thereof in a horizontal direction of <FIG>.

The PCM switch device of <FIG> includes phase change material <NUM>, electrodes 13A, 13B and heater <NUM> as already explained referring to <FIG>. An electrically insulating but thermally conducting layer <NUM> is provided between heater <NUM> and phase change material <NUM> to provide thermal coupling and electric isolation.

In the comparative example of <FIG>, heater <NUM> is a conventional heater which always has a comparatively low electrical resistance, for example below 50Ω, irrespective of a state the phase change switch device is in.

For an off state of the phase change switch device, parasitic capacitances are shown in <FIG>. C<NUM> is a parasitic capacitance between first electrode 13A and second electrode 13B, C<NUM> is a parasitic capacitance between first electrode 13A or a part of phase change material <NUM> close to electrode 13A remaining electrically conducting and heater <NUM>, and C<NUM> is a similar capacitance between electrode 13B or a electrically conducting portion of phase change material <NUM> adjacent to electrode 13B and heater <NUM>. In other words, as heater <NUM> is electrically conducting also in the off state, it effectively acts as a capacitor plate. In case the switch is on and phase change material <NUM> is electrically conducting, still parasitic capacitances remain between phase change material <NUM> and heater <NUM>, with layer <NUM> serving as electrically isolating layer therebetween.

<FIG> shows an equivalent circuit illustrating the parasitic capacitances discussed above with respect to <FIG> in an equivalent circuit diagram. P<NUM> and P<NUM> are terminals corresponding to the first and second electrodes 13A, 13B, respectively.

As mentioned above, in some applications like antenna tuning applications, it is desirable to reduce the off capacitance as much as possible.

<FIG> show a phase change device according to an embodiment in an off state, <FIG> showing a top view and <FIG> showing a cross-sectional view, similar to the comparative example of <FIG>. Here, the heater is in the second state above, illustrated as having a high ohmic resistance(e.g. electrically insulating) portion <NUM> with electrical contact portions <NUM>. This leads to a "replacement" of parasitic capacitances C<NUM>, C<NUM> of <FIG> and <FIG> with a capacitance C<NUM>,<NUM> in parallel to the capacitance C<NUM> of <FIG> and <FIG>, which in <FIG> is labelled C<NUM>,<NUM>. C<NUM>,<NUM> is lower than the series connection of C<NUM> and C<NUM> via heater <NUM> shown in <FIG> and <FIG>, such that the overall capacitance is lower.

Next, various implementation examples of a heater that may change between the first state and the second state will be discussed. First, with reference to <FIG> (including Subfigures 5A and 5B) and <NUM> (including Subfigures 6A to 6C) an implementation using a pin diode is shown.

<FIG> shows a top view of a PCM switch device according to an embodiment, and <FIG> shows a side view thereof. In the embodiment of <FIG>, the heater is formed by a pin diode including a highly p-doped (p+) portion <NUM>, a highly n-doped (n+) portion <NUM> and an intrinsic (i), i.e. nominally undoped or lightly doped, portion therebetween. Highly doped portions may have a resistivity smaller than 10Ω x cm or dopant concentrations greater than 1x10<NUM>/cm<NUM>, whereas lightly doped portions, for example the intrinsic portions above, may have a resistivity smaller than 100Ω x cm and a dopant concentration smaller than <NUM> x <NUM><NUM>/cm<NUM>, for example smaller than 1x10<NUM>/cm<NUM>.

In the top view of <FIG>, intrinsic portion <NUM> extends over the complete phase change material <NUM>, and portions <NUM>, <NUM> are outside the phase change material <NUM> in the top view. In the embodiment of <FIG>, current flows through the phase change material <NUM> and therefore through the switch device in an on-state essentially from left to right in the view of <FIG>, and through the heater from top to bottom in <FIG> or perpendicular to the drawing plane of <FIG>.

As will be further explained below referring to <FIG>, in the first state mentioned above, for heating of a phase change material <NUM> the pin diode <NUM>, <NUM>, <NUM> is forward biased above the threshold voltage, such that a current flows with relatively low resistance. In the second state mentioned above, i.e. outside heating, the pin diode is reversed bias, leading to a depletion portion essentially without free carriers and therefore correspondingly high ohmic resistance.

<FIG> show a variation of the embodiment of <FIG>. Also in case of <FIG>, the heater is provided as a pin diode, here including a highly p-doped portion <NUM>, an intrinsic portion <NUM> and a highly n-doped portion <NUM>. In contrast to <FIG>, the orientation of the pin diode is rotated by <NUM>° in the top view of <FIG>, such that the current flow through the heater when heating phase change material <NUM> and the current flow through the phase change material from electrode 13A to 13B in an on-state are essentially in the same direction, from left to right in <FIG>.

<FIG> shows an example control for the PCM switch device of <FIG>. An adjustable voltage source <NUM> supplies the heater <NUM>, <NUM>, <NUM>. For heating, as shown in Fig. <NUM> the pin diode forming the heater is forward biased, such that a heater flow iheat flows, causing heat generation and heating of phase change material <NUM>. Outside heating the polarity of voltage source <NUM> is reversed, such that the pin diode is reversed bias and a depletion portion is formed as explained above. Voltage source <NUM> in this case is an example for heater feed/control entity <NUM> of <FIG>.

Heaters as used herein are not restricted to pin diodes. <FIG> illustrate a device according to a further embodiment, where <FIG> illustrates a cross-section of the device, and <FIG> illustrates an example control of the heater of <FIG>.

In <FIG>, the heater is provided as an electrostatically controlled heater similar to a field effect transistor (FET), where the heater includes highly n-doped portions <NUM>, <NUM> with a lightly p-doped portion <NUM> in between. In other embodiments, the polarity may be reversed, i.e. two p-doped portions with a n-doped portion in between. Furthermore, the heater includes a control electrode <NUM>. This control electrode <NUM> operates similar to a gate electrode of a field effect transistor, and by applying an appropriate voltage to control electrode <NUM> as a control signal the resistance of the heater can be changed between the first and second states mentioned above.

It should be noted that also here, the heater may be provided rotated by <NUM>° in a top view, as explained above with reference to <FIG> and <FIG> for the pin diode.

<FIG> illustrates an example control. A first voltage/current source <NUM> is used to apply a heating current for heating the heater and therefore phase change material <NUM>. A second voltage source <NUM> is configured to apply a control voltage to control electrode <NUM> with respect to p-doped portion <NUM>, corresponding to applying an appropriate gate force voltage in conventional field effect transistors. By modifying the voltage, the heater may be set to a high ohmic state (second state above) outside heating phases or a low ohmic state (first state above) during heating. Voltage/Current source <NUM> and voltage source <NUM> are a further example for heater feed/control entity <NUM> of <FIG>.

As already briefly mentioned for <FIG>, in the second state of the heater with the high resistance, in some embodiments the portion of the heater having the high resistance (depletion portion in case of a pin diode or also in case of the field effect transistor like arrangement in <FIG>, as well as for some embodiments described further below), overlaps with the phase change material in a top view, while electrically conducting portions like electrodes, highly doped portions or the like do not overlap with the phase change material, in order to further reduce the capacitance. This concept of overlap is further illustrated in <FIG>.

<FIG> shows a heater corresponding to the heater of <FIG>, with an electrically isolating portion <NUM> which, in <FIG> may correspond to the intrinsic portion in case of the pin diode or the lightly p doped portion for the field effect transistor like implementation, and conducting portions <NUM> correspond to the highly p- or n-doped portions. In the top view of <FIG>, at <NUM> an overlap exists between the top electrode <NUM> and phase change material <NUM>, or at least with portions of the phase change material that are turned amorphous in the switched off state, whereas for the lower electrode <NUM>, at <NUM>, no overlap exists. As mentioned above, in some embodiments such an overlap is avoided altogether avoided (as explained e.g. for <FIG>) to further decrease the parasitic capacitance. It should be noted in the rotated arrangement of <FIG>, electrode <NUM> may e.g. overlap with electrode 13A, 13B in the top view.

In <FIG>, a field effect transistor like heater was illustrated. Further configurations of field effect transistors usable as heaters, as well as contacting thereof, will now be described referring to <FIG>, where <FIG>, <FIG>, <FIG> and <FIG> each include subfigures A and B. Subfigure A in each case shows a cross-sectional view in a first direction, and subfigure B shows a cross-sectional view in a second direction perpendicular to the first direction. For example, given the top views discussed previously, the respective subfigure A may be a cross-section from left to right in the top view, and subfigure B may be a cross-section from top to bottom of the top view.

<FIG> shows an embodiment of a PCM switch device having a field effect transistor as a heater. The PCM switch device of <FIG> is formed on a substrate <NUM>, for example a lightly n-doped semiconductor substrate. A p-doped portion <NUM> is formed in substrate <NUM>. N-doped source and drain portions <NUM>, <NUM> are also formed. Separated from portion <NUM> by a gate oxide, a gate electrode <NUM> is formed, for example made of metal or polysilicon. Separated from gate electrode <NUM> by electrically insulating but thermally conducting material <NUM>, the phase change material <NUM> is deposited. Electrodes 13A, 13B are formed for contacting phase change material <NUM>, and electrodes 95A, 95B are formed for contacting source and drain portions <NUM>, <NUM>, respectively. An additional electrode (not shown in <FIG>) is formed for electrically contacting the gate electrode <NUM>. The structure is enclosed in a dielectric material <NUM>, for example silicone dioxide. Formation of the structure of <FIG>, as with previously discussed PCM devices, may use conventional semiconductor process techniques for depositing the various components in layers (for example the electrodes in metal layers), and/or using doping techniques like diffusion doping or ion implantation to form the portion.

In the first state, for heating the phase change material, electrode <NUM> is controlled such that an n channel indicated by a dashed line <NUM> is formed through which current can flow from electrode 95A to electrode 95B, causing heat generation and heating of phase change material <NUM>.

In the second state outside the heating, the gate may be controlled to cause a high electric resistance between source and drain terminals <NUM>, <NUM>. In some embodiments, the transistor may be a normally off transistor, such that when no voltage is applied the gate electrode, the transistor is in an off state corresponding to the second state having a high resistance.

Reference numeral <NUM> illustrates a parasitic body diode of the transistor, formed between p-doped portion <NUM> and substrate <NUM>.

<FIG> illustrates a variation of the embodiment of <FIG>. <FIG> shows a cross-sectional view corresponding to the view of <FIG>, and <FIG> shows a cross-sectional view corresponding to the cross-sectional view of <FIG>.

Compared to the embodiment of <FIG>, as best seen in <FIG> the source and drain terminals are modified and include highly n-doped portions <NUM>, <NUM>, respectively, and lower doped n-type doped portions <NUM>, <NUM> having a thin somewhat L-shaped shape in cross-section as shown in <FIG>. Portions <NUM>, <NUM> may have a similar doping as substrate <NUM> or may in part B made of substrate <NUM> in a manufacturing process. The configuration of <FIG> compared to the configuration of Fi. <NUM>, may lead to a higher voltage capability of the source and drain terminals versus the gate terminals, i.e. higher voltages may be applied to the PCM switch device for example in an off state.

<FIG> illustrate a further modification of the embodiment of <FIG>, where <FIG> shows a cross-sectional view corresponding to <FIG> and <FIG> shows a cross-sectional view corresponding to <FIG>. Here, instead of a normal substrate like a normal silicone substrate <NUM> a silicon on insulator (SOI) substrate is used, including substrate <NUM> and silicon dioxide layer <NUM>. The devices are then formed on a silicon layer (as a layer not shown in <FIG>, or removed during the processing) on top of silicon dioxide layer <NUM>. In this case no bulk diode <NUM> is formed, which in some cases may improve the high frequency behavior of the switch device.

The embodiments of <FIG> show planar field effect transistor devices. In other embodiments, as a heater a field effect transistor may be provided in a trench within a substrate. Corresponding embodiments will now be described referring to <FIG> including Subfigures 12A and 12B.

In <FIG>, a trench field effect transistor is provided in a trench formed in substrate <NUM>. Gate electrodes 92A, 92B in the cross-section of <FIG> are formed on two sides of p-doped portion <NUM>, leading to the formation of two n-channels in a switched on state for heating as indicated by dashed lines <NUM>. Current trough the heater flows in a horizontal direction in the view of <FIG> or perpendicular to the drawing plane of <FIG>. Electrodes <NUM>, of which one is shown in <FIG>, contact gate electrodes 92A, 92B, and electrodes 95A, 95B as schematically shown contact source and drain portions, which are not explicitly shown in <FIG>. With the arrangement in a trench, the gate electrode is not interposed between the phase change material and the N-channel when heating. Simulations have shown that this may lead to an advantageous heat distribution from heating phase change material <NUM>.

<FIG> illustrates a variation of the embodiment of <FIG> provided on a silicon on insulator substrate including the bulk substrate <NUM>, silicon dioxide layer <NUM> and a silicon layer <NUM> on top of silicon dioxide layer <NUM>.

The field effect transistor is provided in a trench within layer <NUM>. Otherwise, the configuration corresponds to the configuration of the trench transistor of <FIG>. Similar to <FIG>, also here no bulk diode is present.

<FIG> is a flow chart illustrating a method according to an embodiment, which may be used for operating the PCM switch devices of any of the preceding embodiments. To avoid repetitions, the method of <FIG> will be described referring to those embodiments.

At <NUM>, the method comprises setting a heater of a PCM switch device to a low first state having a low electrical resistance for heating the phase change material, in order to perform a set of reset operation. For example, in case the heater is provided as a pin diode, the diode may be forward biased, and when it is provided as a transistor-like structure, a control electrode may be controlled accordingly.

At <NUM>, the method comprises setting the heater to a high resistance second state having a high electrical resistance outside the heating, for example in an off state, on state or both. For example, in case of a pin diode this diode may be reversed biased, or a control electrode of a transistor-like structure may be controlled such that no conductive channel is formed.

The actions at <NUM> and <NUM> may be repeated in any order. For example, the heater may be set to the first, low resistance state at <NUM> any time a set or reset operation and therefore a heating of the phase change material is to be performed.

<FIG> is a flow chart illustrating a method for manufacturing a PCM switch device according to an embodiment, for example for manufacturing any of the embodiments discussed above. Again, the method will be described referring to the previous Figures.

At <NUM> the method comprises providing a phase change material. At <NUM>, the method comprises providing a heater which is switchable between a first state and a second state as explained above in thermal contact with the phase change material. It should be noted that the order of <NUM> and <NUM> may also be reversed such that the heater is first manufactured, followed by the phase change material. For example, in the embodiments discussed above, heater structures may first be formed by deposition, iron implantation and the like, and then the phase change material may be deposited.

<FIG> illustrates an application example of PCM switch devices according to embodiments for antenna tuning purposes. <FIG> illustrates an antenna structure <NUM> including a so called feed point <NUM> and a first aperture point <NUM>. Feed point <NUM> is coupled to a shunt inductor Lshunt and, for tuning purposes, may be selectively coupled via a first switch device SW<NUM> with a parallel circuit of an inductor L<NUM> and a capacitor C<NUM>. Aperture point <NUM> is coupled to an inductor L<NUM> and a capacitor C<NUM> as shown, which may be selectively coupled to ground via a switch device SW<NUM>. Switch devices SW<NUM>, SW<NUM> in an embodiment are implemented using PCM switch devices according to any of the above embodiments. In this way, a parasitic capacitance of switches SW<NUM>,SW<NUM> is reduced, which otherwise could adversely affect the tuning behavior and radio frequency behavior.

Claim 1:
A phase change material switch device (<NUM>), comprising:
a phase change material (<NUM>), and
a heater device (<NUM>; <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; <NUM>, <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; 92A, 92B, <NUM>) thermally coupled to the phase change material (<NUM>),
characterized in that
the heater device (<NUM>; <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; <NUM>, <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; 92A, 92B, <NUM>) is configured to:
have a first electrical resistance in a first state where current is applied to the heater device (<NUM>; <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; <NUM>, <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; 92A, 92B, <NUM>) for heating the phase change material (<NUM>), and
have a second electrical resistance higher than the first electrical resistance in a second state outside heating phases of the heater device (<NUM>; <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; <NUM>, <NUM>, <NUM>, <NUM>; <NUM>-<NUM>; 92A, 92B, <NUM>).