Phase change switch with adhesive layer

Abstract

The invention relates to a phase change switch with an adhesive layer. A semiconductor device includes a semiconductor substrate, a phase change switching device formed over the semiconductor substrate and including a strip of phase change material connected between an RF input contact and an RF output contact and a dielectric material encapsulation layer thermally coupled to the strip of phase change material, the silicon adhesion layer forms a direct interface with the first surface of the strip of phase change material and separates the first surface from the dielectric material formed on the silicon adhesion layer.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductors, and more particularly, to a phase change switch having an adhesion layer. Background Art

[0002] Modern electronic applications require switching devices to be able to accommodate very high frequency signals. For example, fifth generation (5G) wireless applications may operate in a frequency band of approximately 24 GHz (gigahertz) or higher. Maintaining the correct on / off ratio (versus) / insulation vs. insertion loss / R for 5G applications is difficult or impossible in current semiconductor technologies (such as CMOS technology). ON (on resistance) and C OFF (On-capacitance). Phase change switches represent a promising technology that can meet the frequency requirements and insertion loss requirements of 5G applications. Phase change switches operate by modulating the conductive state of the phase change material by heating. Practical RF applications of phase change switches require shrinking size while maintaining low on-resistance of the device. This generates high currents and high heat density, which creates challenges for reliability. Summary of the invention

[0003] A semiconductor device is disclosed. According to an embodiment, the semiconductor device includes: a semiconductor substrate; a phase change switch formed on the semiconductor substrate, the phase change switch device including a phase change material strip connected between an RF input contact and an RF output contact and a heating element thermally coupled to the phase change material strip; and a silicon adhesion layer forming a direct interface with a first surface of the phase change material strip and separating the first surface from a dielectric material formed on the silicon adhesion layer.

[0004] A method for forming a semiconductor device is disclosed. According to an embodiment, the method includes: providing a semiconductor substrate; forming a phase change switch device on the semiconductor substrate, the phase change switch device including a phase change material strip connected between an RF input contact and an RF output contact and a heating element thermally coupled to the phase change material strip; and forming a silicon adhesion layer that forms a direct interface with a first surface of the phase change material strip and separates the first surface from a dielectric material formed on the silicon adhesion layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The elements of the drawings are not necessarily drawn to scale with each other. Similar reference numerals identify corresponding similar parts. Unless they mutually exclude each other, the features of the various illustrated embodiments may be combined. The embodiments are depicted in the drawings and described in detail in the following description.

[0006] Figure 1 A cross-sectional view of a PCM (Phase Change Material) switchgear according to an embodiment is illustrated.

[0007] Figure 2An enlarged view of a PCM switchgear according to an embodiment is illustrated. DETAILED DESCRIPTION

[0008] Embodiments of PCM (phase change material) switch devices and corresponding methods of forming PCM switch devices are disclosed herein. PCM switch devices are embedded in dielectric materials (such as silicon dioxide (SiO2), silicon nitride (SiN), silicon oxynitride (SiO X N Y )). This fabrication technique allows the PCM switching device to be fabricated on a semiconductor substrate using standard photolithography techniques and provided within an interconnection region formed in a so-called back-end-of-line processing step, thereby allowing easy interconnection with other devices formed on or within the semiconductor substrate. However, one challenge associated with embedding the PCM switching device in a dielectric material is that delamination may occur between the dielectric material and the phase change material. The embodiments disclosed herein provide an adhesion layer that directly interfaces with the phase change material of the PCM switching device and separates the phase change material from any region or layer of dielectric material formed on the adhesion layer. The adhesion layer provides a stable interface when at high temperatures and therefore mitigates delamination. The thickness and material composition of the adhesion layer are tailored to ensure that the adhesion layer does not introduce leakage paths that have a significant detrimental effect on the off-state performance of the device.

[0009] refer to Figure 1 , the semiconductor device 100 includes a PCM switch device 126 formed on a semiconductor substrate 102. The semiconductor substrate 102 can be any type of substrate compatible with semiconductor processing techniques (including lithography and the formation and structuring of phase change materials). For example, the semiconductor substrate 102 can be a commercially available bulk semiconductor wafer (e.g., a silicon wafer or a so-called SOI substrate (silicon on insulator) wafer). Other types of semiconductors (such as silicon carbide (SiC), silicon germanium (SiGe), III-V type semiconductors, etc.) can be present in the semiconductor substrate 102 and / or form the base material of the semiconductor substrate 102. In other examples, the semiconductor substrate 102 may include other materials (e.g., glass, quartz, sapphire, etc.).

[0010] According to an embodiment, the semiconductor substrate 102 is configured with semiconductor mesas that are laterally insulated from each other by dielectric regions, the dielectric regions comprising, for example, silicon dioxide, silicon nitride, silicon oxide nitride, etc. The semiconductor substrate 102 may be processed by a so-called STI (shallow trench insulation) technique, wherein the dielectric regions correspond to trenches that are etched and filled with dielectric material. Alternatively, a similar structure may be realized using a so-called SOI (silicon on insulator) substrate, wherein the semiconductor mesas correspond to semiconductor material regions that are epitaxially grown between buried insulator portions of the semiconductor substrate.

[0011] The PCM switchgear 126 includes a phase change material strip 128. The phase change material strip 128 is formed of a material that can transition between two different phases, each having a different electrical conductivity. For example, the phase change material strip 128 can include a material that changes from an amorphous state to a crystalline state based on the application of heat to the phase change material, wherein the phase change material is electrically insulating (i.e., blocking electrical connections) in the amorphous state and conductive (i.e., providing a low resistance current path) in the crystalline state. Examples of phase change materials with this property include chalcogenides and chalcogenide alloys. In particular, these phase change materials can include germanium antimony telluride (GST), germanium telluride, and germanium antimony.

[0012] The PCM switchgear 126 additionally includes a heating element 130. The heating element 130 is formed of a conductive or semi-conductive material that converts electrical energy into heat by ohmic heating. Examples of such materials include nickel, chromium, molybdenum, tungsten, platinum, and alloys thereof. The heating element 130 may be an elongated structure that extends transversely to the direction of current flow of the phase change material and is disposed in contact with the phase change material. Figure 1 The heating element 130 is thermally coupled to the phase change material strip 128. This means that the heating element 130 is close enough to the phase change material strip 128 to quickly transfer heat in the above-mentioned manner to change the conductive state of the phase change material strip 128. An intermediate material can be arranged between the heating element 130 and the phase change material strip 128 in a thermally coupled arrangement, wherein the intermediate material is thin enough and / or thermally conductive to enable effective heat transfer. For example, in the described embodiment, an insulating pad 132 is inserted between the heating element 130 and the phase change material strip 128. The insulating pad 132 electrically insulates the heating element 130 from the phase change material strip 128 while allowing a large amount of heat transfer between the two. To this end, the insulating pad 132 can be a relatively thin (e.g., less than 1 μm thick, such as a thickness between 25 nm and 200 nm, such as a thickness between 50 nm and 100 nm) dielectric material (e.g., silicon dioxide, silicon nitride, silicon oxide nitride, AlN, etc.) layer.

[0013] The PCM switch device 126 additionally includes an RF input contact 129 and an RF output contact 131. The RF input contact 129 and the RF output contact 131 are each formed of a conductive material (e.g., metals such as copper, aluminum, nickel, chromium, molybdenum, tungsten, platinum, titanium, and alloys thereof, and doped polycrystalline materials). The RF input contact 129 and the RF output contact 131 can be formed of the same material as the heating element 130. However, this is not necessary. The RF input contact 129 and the RF output contact 131 each make ohmic contact with the phase change material strip 128 at opposite ends.

[0014] The working principle of the PCM switch device 126 is as follows. The PCM switch device 126 is a lateral device, which is configured to conduct parallel to the main surface of the semiconductor substrate 102. The heating element 130 is configured to control the conductive connection between the RF input contact 129 and the RF output contact 131. The heating element 130 controls this conductive connection by applying heat to the phase change material strip 128. In the off state of the PCM switch device 126, the phase change material strip 128 is in an amorphous state or a partially amorphous state. Therefore, the phase change material strip 128 blocks the voltage maintained between the RF input contact 129 and the RF output contact 131. In the on state of the PCM switch device 126, the phase change material strip 128 is in a crystalline state. Therefore, the phase change material strip 128 provides a low resistance electrical connection between the RF input contact 129 and the RF output contact 131. Therefore, in this state, current can flow laterally through the phase change material strip 128. The PCM switch device 126 performs a switching operation by heating the phase change material strip 128 using the heating element 130. The phase change material can be transitioned to an amorphous state by applying a short pulse of high intensity heat (e.g., a pulse in the range of 50-1000 nanoseconds) so that the phase change material reaches a melting temperature (e.g., in the range of 600°C to 750°C) and then rapidly cooling the material. This is referred to as a "reset pulse". The phase change material of the phase change material strip 128 can be transitioned to a crystalline state by applying a longer duration pulse of lower intensity heat (e.g., in the range of 0.5-10 microseconds) so that the phase change material reaches a temperature at which the material rapidly crystallizes and is highly conductive (e.g., in the range of 250°C to 350°C). This is referred to as a "set pulse".

[0015] The PCM switch device 126 may be formed according to the following steps. First, a semiconductor substrate 102 is provided, and a base layer 133 of a dielectric material (e.g., silicon dioxide, silicon nitride, silicon oxynitride, etc.) is formed on a major surface of the semiconductor substrate 102. Grooves are formed in the dielectric material base layer 133, and the RF input contact 129, the RF output contact 131, and the heating element 130 are formed in these grooves. A common metal layer that is conformally deposited and then planarized may form each of these structures. In other embodiments, the RF input contact 129 and the RF output contact 131 as the heating element 130 are formed by separate deposition steps, and thus may have different material compositions. Subsequently, a thin dielectric layer including, for example, silicon dioxide, silicon nitride, silicon oxynitride, etc. is formed over the RF input contact 129, the RF output contact 131, and the heating element 130. The thin dielectric layer may be patterned to expose the RF input contact 129 and the RF output contact 131 from above, while providing an insulating pad 132 over the heating element 130. Subsequently, a phase change material layer is conformally deposited to contact the RF input contact 129 and the RF output contact 131. The phase change material layer may be deposited as will be referred to below. Figure 2 The capping structure layer 135 is further described in detail. Subsequently, an etching process may be performed to structure the layer of phase change material into phase change material strips 128 and any layers used to form the capping structure 135. As shown, the PCM switch device 126 additionally includes an encapsulation layer 137 of a dielectric material (e.g., silicon dioxide, silicon nitride, silicon nitride, etc.) formed over the capping structure 135 and laterally surrounding the PCM switch device 126. The encapsulation layer 137 may be a relatively thick (e.g., 100nm to 200nm thick) region that includes a dielectric material layer used as a hard mask for patterning the phase change material, and optionally, may include an additional layer of dielectric material formed after the etching process to provide additional encapsulation after the etching is completed.

[0016] The semiconductor device additionally includes an interconnection region 106 formed above the PCM switch device 126. The interconnection region 106 is electrically insulated from the PCM switch device 126 and is used to electrically connect the PCM switch device 126 to other devices and / or externally accessible terminals on the outer surface of the semiconductor device. In particular, the RF input contact 129 and the RF output contact 131 can be routed to externally accessible bonding pads (not shown) via the interconnection region 106. The interconnection region 106 includes a metallization layer 108 formed of, for example, copper, aluminum, nickel, etc. and alloys thereof, which is structured into conductive tracks and routed along a wiring plane to form electrical interconnections. The interconnection region 106 additionally includes an interlayer dielectric region 110 formed of an electrically insulating material such as silicon dioxide, silicon nitride, silicon oxynitride, glass, polymers, etc., and vias extending through one or more interlayer dielectric regions 110 and providing vertical connections between various metallization levels.

[0017] refer to Figure 2 A close-up view of a PCM switch device 126 is shown. The PCM switch device 126 includes a capping structure 135. The capping structure 135 is partially formed on the phase change material strip 128. That is, the capping structure 135 does not extend beyond the outer edge of the phase change material strip 128. As mentioned above, the capping structure layer 135 and the phase change material can be etched simultaneously, thus making the capping structure 135 and the phase change material strip 128 coextensive with each other.

[0018] The cap structure 135 includes an adhesion layer 145. The adhesion layer 145 forms a direct interface with the first surface 147 of the phase change material strip 128. That is, the adhesion layer 145 directly contacts the first surface 147 of the phase change material strip 128. In the depicted embodiment, the first surface 147 of the phase change material strip 128 corresponds to an upper surface opposite to the semiconductor substrate 102. The adhesion layer 145 separates the first surface 147 from any dielectric material on the adhesion layer 145. That is, the adhesion layer 145 is interposed between the first surface 147 of the phase change material 128 and any dielectric region or layer formed on the adhesion layer 145. For example, the adhesion layer 145 can contact the first surface 147 with SiO2, SiN, SiO X N Y 、Me x O y 、Me x N y 、Me x O y N zIn the depicted embodiment, the capping structure 135 additionally includes a dielectric capping layer 149 formed on the adhesion layer 145. Thus, the adhesion layer 145 separates the first surface 147 of the phase change material strip 128 from the dielectric capping layer 149. The dielectric capping layer 149 may be a layer including, for example, silicon dioxide, silicon nitride, silicon oxynitride, etc. The thickness of the dielectric capping layer 149 may be on the order of 10 nm to less than 1 μm.

[0019] For example, during subsequent processing steps, such as thermal oxidation, testing, etc., and / or during operation of the PCM switch device 126, the phase change material 128 may be subjected to high temperatures (e.g., temperatures of 300°C, 400°C, 500°C, or higher). These high temperatures may cause delamination at the surface of the PCM switch device 126. Specifically, due to differences in CTE (coefficient of thermal expansion), for example, the dielectric material formed on the PCM switch device 126 may delaminate from the phase change material strips 128. Under these conditions, the adhesion layer 145 has a material composition that provides better adhesion to the phase change material than the dielectric material. For example, the adhesion layer 145 can be formed of a semiconductor material that has a CTE that is more matched to the phase change material than the dielectric material. Examples of these semiconductor materials include silicon, carbon, germanium, gallium, tantalum, aluminum, and alloys or compounds thereof. The adhesion layer 145 can be formed by semiconductor deposition techniques (such as atomic layer deposition, epitaxy, etc.).

[0020] According to an embodiment, the resistance of the adhesion layer 145 is at least 10 times greater than the resistance of the phase change material strip 128 between the RF input contact 129 and the RF output contact 131. 5 Ω. For example, the resistance of the adhesion layer 145 may be greater than 1×10 5 Ω and 5×10 6 Ω. By maintaining this relationship between the resistance of the adhesion layer 145 and the phase change material, the off resistance of the PCM switch device 126 is advantageously maintained high. In more detail, the adhesion layer 145 represents a potential shunting path for current to flow between the RF input contact 129 and the RF output contact 131, bypassing the voltage block provided by the phase change material strip 128. Maintaining a high resistivity of the adhesion layer 145 can mitigate this shunting effect and prevent the off state leakage of the device.

[0021] According to an embodiment, the adhesion layer 145 is a silicon layer (i.e., an elemental silicon layer). The silicon adhesion layer 145 can be formed to be very thin (e.g., on the order of 2 nm to 20 nm). In an embodiment, the thickness of the silicon adhesion layer 145 is no greater than 15 nm and may be no greater than 10 nm or less. By providing a silicon adhesion layer 145 having these thickness values, the adhesion layer 145 can both significantly mitigate delamination and meet the above-mentioned resistivity requirements for maintaining the off-state leakage of the device at an acceptable level. Stated in another way, reducing the thickness of the adhesion layer 145 reduces the cross-sectional area and thus reduces the resistance. Similar principles can be used to control the thickness of other types of materials to meet the above-mentioned resistivity requirements. The adhesion layer 145 can have an almost constant thickness throughout the length of the adhesion layer 145. In the presence of any thickness variation, the above-mentioned thickness values ​​may refer to the maximum thickness of the adhesion layer 145. In addition, where possible at the thickness values ​​mentioned above, the adhesion layer 145 is preferably formed with a low doping level (e.g., an intrinsic level) and has a single crystal crystal structure as much as possible at the above-mentioned thickness values ​​to maintain low resistivity.

[0022] In addition to the semiconductor device 100 depicted, embodiments of the phase change switch device can also have many different configurations and obtain the advantageous lamination relief provided by the adhesion layer as described herein. In general, these devices include any configuration in which the phase change switch device is embedded in a dielectric material, and the adhesion layer described herein is inserted between the surface of the phase change material and the dielectric material. For example, the dielectric cap layer 149 from the cap structure 135 can be omitted. In this case, the first surface 147 of the phase change material strip 128 can be separated from the dielectric material (e.g., the dielectric material of the encapsulation layer 137 or any other dielectric region formed on the adhesion layer 145) using the corresponding adhesion layer 145. The adhesion layer can be applied to different surfaces of phase change materials with different configurations. For example, depending on the configuration of the device, a corresponding adhesion layer 145 can be provided on the lower side of the phase change material strip facing the semiconductor substrate, and the phase change material strip can be separated from any underlying dielectric material using it. Individually or in combination, the arrangement of elements in the phase change switch device can be different from the described embodiments. For example, electrical contact with the phase change material strip 128 can be achieved at the upper side of the phase change material strip opposite the semiconductor substrate. Alone or in combination, the heating element 130 can be arranged on the upper side of the phase change material strip opposite the semiconductor substrate 102, or can be arranged to face multiple sides of the phase change material strip.

[0023] While not so limiting the present disclosure, the following numbered examples illustrate one or more aspects of the present disclosure.

[0024] Embodiment 1. A semiconductor device comprises: a semiconductor substrate; a phase change switch device formed on the semiconductor substrate, the phase change switch device comprising a phase change material strip connected between an RF input contact portion and an RF output contact portion, and a heating element thermally coupled to the phase change material strip; and a silicon adhesion layer, which forms a direct interface with a first surface of the phase change material strip and separates the first surface from a dielectric material formed on the silicon adhesion layer.

[0025] Embodiment 2. The semiconductor device of embodiment 1, wherein the resistance of the silicon adhesion layer is at least 10 times greater than the resistance of the phase change material strip between the RF input contact and the RF output contact. 5 Ω.

[0026] Embodiment 3. The semiconductor device of Embodiment 2, wherein the thickness of the silicon adhesion layer is less than or equal to 20 nm.

[0027] Embodiment 4. The semiconductor device of embodiment 1, wherein the silicon adhesion layer separates the first surface from a dielectric material comprising any one of: SiN, SiO2, and SiO X N Y .

[0028] Embodiment 5. The semiconductor device according to embodiment 1, wherein the semiconductor device includes a cap structure locally formed on the phase change material strip, wherein the cap structure includes a silicon adhesion layer and a dielectric cap layer, and wherein the silicon adhesion layer separates the first surface from the dielectric cap layer.

[0029] Embodiment 6. The semiconductor device of embodiment 5, wherein the dielectric capping layer is a SiN layer.

[0030] Embodiment 7 The semiconductor device of Embodiment 5, wherein the semiconductor device further comprises an encapsulation layer of dielectric material formed over the cap structure and laterally surrounding the phase change switch device.

[0031] Embodiment 8 The semiconductor device of Embodiment 1, wherein the phase change switching device is a lateral device configured to conduct parallel to a major surface of the semiconductor substrate.

[0032] Embodiment 9 The semiconductor device of Embodiment 8, wherein the first surface of the phase change material strip is an upper surface of the phase change material strip facing away from the major surface.

[0033] Embodiment 10 The semiconductor device of Embodiment 8, wherein the RF input contact, the RF output contact, and the heating element region are each disposed below the phase change material strip.

[0034] Embodiment 11. A method for forming a semiconductor device, the method comprising: providing a semiconductor substrate; forming a phase change switch device on the semiconductor substrate, the phase change switch device comprising a phase change material strip connected between an RF input contact portion and an RF output contact portion, and a heating element thermally coupled to the phase change material strip; and forming a silicon adhesion layer, which forms a direct interface with a first surface of the phase change material strip and separates the first surface from a dielectric material formed on the silicon adhesion layer.

[0035] Embodiment 12. The method of Embodiment 11, wherein the resistance of the silicon adhesion layer is at least 10 5 Ω greater than the resistance of the phase change material strip between the RF input contact and the RF output contact.

[0036] Embodiment 13. The method of embodiment 11, wherein the thickness of the silicon adhesion layer is less than or equal to 20 nm.

[0037] Embodiment 14. The method of embodiment 11, wherein the silicon adhesion layer separates the first surface from a dielectric material comprising any one of: SiN, SiO2, and SiO X N Y .

[0038] Embodiment 15. The method of embodiment 11, further comprising locally forming a capping structure on the phase change material strip, wherein the capping structure comprises a silicon adhesion layer and a dielectric capping layer, and wherein the silicon adhesion layer separates the first surface from the dielectric capping layer.

[0039] Embodiment 16. The method of Embodiment 15, wherein the dielectric capping layer is a SiN layer.

[0040] Embodiment 17 The method of Embodiment 15 further comprising forming a dielectric material of an encapsulation layer above the cap structure and laterally surrounding the phase change switch device.

[0041] Embodiment 18 The method of Embodiment 11, wherein the phase change switching device is a lateral device configured to conduct parallel to a major surface of the semiconductor substrate.

[0042] Embodiment 19. The method of Embodiment 18, wherein the first surface of the phase change material strip is an upper surface of the phase change material strip facing away from the major surface.

[0043] Embodiment 20. The method of Embodiment 18, wherein the RF input contact, the RF output contact, and the heating element zone are each disposed below a strip of phase change material.

[0044] The term "electrically connected" as used herein describes a permanent low-impedance connection between electrically connected elements, such as direct contact between the relevant elements or a low-impedance connection via metal and / or highly doped semiconductor.

[0045] As used herein, the terms "having", "containing", "including", "comprising" and the like are open terms that indicate the presence of stated elements or features, but do not exclude additional elements or features. The articles "a", "an" and "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

[0046] It should be understood that, unless specifically stated otherwise, the features of the various embodiments described herein may be combined with each other.

[0047] Although specific embodiments have been illustrated and described herein, it will be appreciated by those skilled in the art that various alternative and / or equivalent embodiments may replace the specific embodiments shown and described without departing from the scope of the present invention. The present application is intended to cover any adjustments or changes to the specific embodiments discussed herein. Therefore, the present invention is intended to be limited only by the claims and their equivalents.

Claims

1. A semiconductor device comprising: Semiconductor substrate; a phase change switch device formed on the semiconductor substrate, the phase change switch device comprising a phase change material strip connected between an RF input contact and an RF output contact, and a heating element thermally coupled to the phase change material strip; as well as A silicon adhesion layer forms a direct interface with the first surface of the phase change material strip and separates the first surface from a dielectric material formed on the silicon adhesion layer.

2. The semiconductor device of claim 1 , wherein the resistance of the silicon adhesion layer is at least 10 times greater than the resistance of the phase change material strip between the RF input contact and the RF output contact. 5 Ω. 3 . The semiconductor device according to claim 2 , wherein a thickness of the silicon adhesion layer is less than or equal to 20 nm.

4. The semiconductor device of claim 1 , wherein the silicon adhesion layer separates the first surface from the dielectric material comprising any one of: SiN, SiO 2 , and SiO X N Y .

5. The semiconductor device of claim 1 , wherein the semiconductor device comprises a cap structure locally formed on the phase change material strip, wherein the cap structure comprises the silicon adhesion layer and a dielectric cap layer, and wherein the silicon adhesion layer separates the first surface from the dielectric cap layer. The semiconductor device of claim 5 , wherein the dielectric capping layer is a SiN layer. 7 . The semiconductor device of claim 5 , wherein the semiconductor device further comprises an encapsulation layer of dielectric material formed over the cap structure and laterally surrounding the phase change switch device. 8 . The semiconductor device of claim 1 , wherein the phase change switching device is a lateral device configured to conduct parallel to a major surface of the semiconductor substrate. 9 . The semiconductor device of claim 8 , wherein the first surface of the phase change material strip is an upper surface of the phase change material strip facing away from the major surface.

10. The semiconductor device of claim 8, wherein the RF input contact, the RF output contact, and the heating element region are each disposed below the phase change material strip.

11. A method of forming a semiconductor device, the method comprising: providing a semiconductor substrate; forming a phase change switching device over the semiconductor substrate, the phase change switching device comprising a phase change material strip connected between an RF input contact and an RF output contact, and a heating element thermally coupled to the phase change material strip; as well as A silicon adhesion layer is formed that directly interfaces with the first surface of the phase change material strip and separates the first surface from a dielectric material formed on the silicon adhesion layer.

12. The method of claim 11, wherein the resistance of the silicon adhesion layer is at least 10 times greater than the resistance of the phase change material strip between the RF input contact and the RF output contact. 5 Ω. The method of claim 11 , wherein the thickness of the silicon adhesion layer is less than or equal to 20 nm.

14. The method of claim 11, wherein the silicon adhesion layer separates the first surface from the dielectric material comprising any one of: SiN, SiO2, and SiO X N Y .

15. The method of claim 11, further comprising locally forming a capping structure on the phase change material strip, wherein the capping structure comprises the silicon adhesion layer and a dielectric capping layer, and wherein the silicon adhesion layer separates the first surface from the dielectric capping layer. The method of claim 15 , wherein the dielectric capping layer is a SiN layer.

17. The method of claim 15, further comprising forming an encapsulating layer of dielectric material over the cap structure and laterally surrounding the phase change switch device.

18. The method of claim 11, wherein the phase change switching device is a lateral device configured to conduct parallel to a major surface of the semiconductor substrate.

19. The method of claim 18, wherein the first surface of the phase change material strip is an upper surface of the phase change material strip facing away from the major surface.

20. The method of claim 18, wherein the RF input contact, the RF output contact, and the heating element zone are each disposed beneath the phase change material strip.

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