Preparation method of phase change radio frequency switch based on heater out-of-plane structure and low parasitic capacitance

Abstract

The application discloses a kind of based on heater low parasitic capacitance phase change radio frequency switch of heterostructure and preparation method, the radio frequency switch includes substrate, a layer of phase change material layer, a layer of heating element layer, a layer of thermal insulation layer, a layer of passivation layer and a layer of radio frequency transmission layer.Heating element under phase change material layer first extends laterally outward, then penetrates substrate with the terminal circuit of heating element using through-silicon via technology, so that the terminal circuit of heating element is located below heating element.The terminal circuit of heating element is located in different interlayer level relative to phase change material layer and radio frequency transmission layer, finally realizes the purpose of reducing parasitic capacitance, improves the radio frequency transmission performance of overall device.

Description

Technical Field

[0001] This invention relates to the field of phase-change radio frequency switch fabrication technology, specifically to an embedded indirect heating Ge-Sb-Te based phase-change radio frequency switch and its fabrication method, which has advantages such as simple process, low cost, fast switching speed, small size, long life, simple structure, easy integration with CMOS and easy packaging. Background Technology

[0002] Phase-change radio frequency (RF) switches utilize the significant resistivity change of chalcogenide compounds between their crystalline and amorphous states in RF circuits. Phase-change films exhibit very high resistivity in their amorphous state and very low resistivity in their crystalline state, with the resistivity change reaching four to five orders of magnitude. When the film is in a high-resistivity state, it isolates the RF signal, reflecting it back to the input terminal and preventing further transmission, thus placing the switch in the off state. When the film is in a low-resistivity state, the RF signal can pass through the phase-change film smoothly, placing the switch in the on state. Given the increasing reliance on RF communication, the demand for high-performance phase-change RF switching devices is growing rapidly. However, the heating elements and circuits in phase-change RF switches often generate parasitic effects related to the RF frequency, leading to performance degradation, such as insertion loss in the ON state and parasitic capacitance (C) in the OFF state. off Phase change RF switches suffer from attenuation, especially when they are primarily designed around thermal performance. Therefore, in large-scale manufacturing of phase change RF switches, practicality is often traded for the ability to control device characteristics and critical dimensions. Summary of the Invention

[0003] In view of the shortcomings of existing RF switch heating methods, the purpose of this invention is to provide a method for reducing parasitic capacitance of phase-change RF switches based on an off-plane heater configuration, providing a new approach for the development of next-generation RF switches. The phase-change RF switch of this invention uses embedded indirect heating. Through-silicon via (TSV) technology, a structure is achieved where the heater path, phase-change material layer, and RF transmission path are not on the same horizontal plane, thereby reducing parasitic capacitance and improving the overall RF transmission performance of the device. This invention can reliably reduce parasitic capacitance, enabling the phase-change RF switch to have low insertion loss and low OFF-state parasitic capacitance (C). off ).

[0004] The specific technical solution for achieving the objective of this invention is as follows:

[0005] A method for fabricating a low parasitic capacitance phase-change radio frequency switch based on a heater-based non-planar structure, comprising the following specific steps:

[0006] The first step involves selecting a single-sided oxidized high-resistivity single-crystal Si substrate, cleaning it, and then patterning it using electron beam lithography. A 200-500 nm deep trench is then etched using reactive ion etching. Following this, a 200-500 nm thick Cr or W metal heating electrode and markings for the next layer are deposited by electron beam evaporation, ensuring that the trench depth and heating electrode thickness are equal. The elongated portion of the heating electrode is the heating region, specifically 0.5-1 μm wide and 5-20 μm long. The heating layer is then removed and cleaned.

[0007] The second step is to deposit a 50-200nm thick SiO2 or Ta2O5 heat insulation layer on the upper surface of the heating layer by magnetron sputtering, and then remove the adhesive and clean to obtain the heat insulation layer.

[0008] The third step involves aligning the cross marks on the upper surface of the heat insulation layer with electron beam lithography to create a pattern. Then, a 100–200 nm thick Ge-Sb-Te-based phase change material and the next layer of lithographic marks are deposited using pulsed laser. The resist is then removed and the layer is cleaned to obtain the phase change layer.

[0009] The fourth step involves aligning the phase transition layer with cross-shaped markings on the upper surface using electron beam lithography to create a pattern. Then, thermal evaporation is used to deposit Cr / Au as the radio frequency transmission layer. The Cr layer has a thickness of 7–20 nm, which serves to increase electrode adhesion. The Au layer has a thickness of 100–200 nm. After removing the resist and cleaning, the radio frequency transmission layer is obtained.

[0010] The fifth step involves depositing a 50-200 nm thick layer of silicon nitride or titanium nitride on the surface of the phase change layer by magnetron sputtering. After alignment with cross marks, the layer is patterned by electron beam lithography. Then, it is etched to the radio frequency transmission layer by reactive ion etching. Finally, a 50-200 nm thick layer of Cu is thermally evaporated and deposited as the pressure contact for the radio frequency transmission electrode. The layer is then cleaned to obtain the passivation layer.

[0011] The sixth step involves protecting the upper surface with epoxy resin or paraffin, followed by chemical mechanical polishing of the lower surface of the substrate to thin the Si substrate to a maximum of 150 μm.

[0012] Step 7: Based on the cross mark on the upper surface of the passivation layer, after aligning with the double-sided alignment process, ultraviolet light is used to etch the pattern on the lower surface of the substrate. Then, deep reactive ion etching is performed on the lower surface of the substrate to etch through to the heating electrode pressure contact to obtain a silicon via. After that, metal material is electroplated to fill the silicon via, the resist is removed and cleaned, and Au metal contacts are ultrasonically spot-welded at the via on the back side to obtain a low parasitic capacitance phase change RF switch based on the heater's non-planar structure.

[0013] The resistivity of the single-sided oxidized high-resistivity single-crystal Si substrate is at least 10000 Ω·cm, and the thickness of the surface oxide layer is at least 100 nm.

[0014] The contact area between the through-silicon via and the heating electrode is at least 10 μm * 10 μm.

[0015] The Ge-Sb-Te based phase change material is Ge2Sb2Te5, Sb2Te3, Sb2Te, GeSb2Te4, or GeTe. The pressure contact area of ​​the upper surface radio frequency transmission electrode is at least 50 μm * 50 μm.

[0016] The area of ​​the Au metal contact at the silicon through-hole on the lower surface is at least 50 μm*50 μm.

[0017] The metal material used to fill the through-silicon via is Cu.

[0018] A low parasitic capacitance phase-change radio frequency switch based on a heater-plane structure, fabricated by the above method.

[0019] Compared with the prior art, the biggest advantage of this invention is that the phase change radio frequency switch in the embodiment of this invention is processed using mature silicon semiconductor technology, the device is heated by embedded indirect heating, and silicon through-hole technology is used to make the terminal circuit of the heating element located at a different level relative to the phase change material layer and the radio frequency transmission layer, thereby reducing parasitic capacitance and improving the overall radio frequency transmission performance of the device. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the implementation process of a fabrication method for a low parasitic capacitance phase-change radio frequency switch based on a heater-based non-surface structure, provided in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of a longitudinal section of the Cr heating electrode provided in an embodiment of the present invention;

[0022] Figure 3 This is a cross-sectional schematic diagram of the Cr heating electrode provided in an embodiment of the present invention;

[0023] Figure 4 This is a cross-sectional schematic diagram of the heat insulation layer provided in an embodiment of the present invention;

[0024] Figure 5 This is a cross-sectional schematic diagram of the phase change material thin film provided in an embodiment of the present invention;

[0025] Figure 6 This is a cross-sectional schematic diagram of the radio frequency transmission electrode provided in an embodiment of the present invention;

[0026] Figure 7 This is a cross-sectional schematic diagram of the passivation layer and the radio frequency transmission electrode pressure contact provided in an embodiment of the present invention;

[0027] Figure 8 This is a schematic longitudinal section of the phase-change radio frequency switch according to an embodiment of the present invention;

[0028] Figure 9 This is a perspective view of a low parasitic capacitance phase-change radio frequency switch based on a heater-type non-surface structure according to an embodiment of the present invention;

[0029] Figure 10 This is a simulation comparison of the insertion loss performance of a phase-change RF switch with low parasitic capacitance based on a heater-out-of-plane structure and a phase-change RF switch with a heater-coplanar structure in the DC-40GHz frequency range, according to an embodiment of the present invention. Detailed Implementation

[0030] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0031] To illustrate the technical solution described in this invention, specific embodiments are described below.

[0032] Figure 1 The following is a schematic diagram illustrating the implementation process of a fabrication method for a low parasitic capacitance phase-change radio frequency switch based on a heater-based non-surface structure, as provided in an embodiment of the present invention.

[0033] Step 101: Select a single-sided oxidized high-resistivity single crystal Si as the substrate. After cleaning, it is patterned by electron beam lithography. Then, a 200nm deep trench is etched by reactive ion etching. Immediately afterwards, a 200nm thick Cr or W metal heating electrode and the marking for the next layer are deposited by electron beam evaporation. This ensures that the trench depth and the heating electrode thickness are the same. The slender part of the heating electrode is the heating area, with a specific size of 1μm wide and 20μm long. The heating layer is obtained by removing the resist and cleaning.

[0034] Optionally, the resistivity of the single-sided oxidized high-resistivity single-crystal Si substrate is at least 10000 Ω·cm, and the thickness of the surface oxide layer is 300 nm.

[0035] Optionally, the high-resistivity single-crystal Si substrate adopts the (100) crystal orientation. A fundamental characteristic of crystals is their directionality; crystal properties differ along different directions of the lattice. The lattice points of a Bravais lattice can be viewed as arranged in a series of parallel straight lines, which are called crystal rows. The same lattice point can form crystal rows with different orientations, and each crystal row defines a direction called a crystal orientation. Here, the (100) crystal orientation refers to the atoms that pass through the origin and the straight line passing through the points x=1, y=0, z=0;

[0036] like Figure 2 and Figure 3 The schematic diagram of the Cr heating electrode shown indicates that the size L of the heating region 51 is... heater 20μm, W heater 1μm, thickness T heater The wavelength is 200nm, and the external electrode contact is square with a side length D. heater The bridging length H between the heating region and the 50μm region is [missing information]. heater The thickness is 10 μm. W, TiN, TiW, NiCr, NiCrSi and Ta are also commonly used heating electrode materials, and they have resistivity similar to Cr, so they can also be used to replace the original Cr heating layer.

[0037] Step 102: A 50nm thick SiO2 heat insulation layer is deposited on the upper surface of the heating layer by magnetron sputtering, and the heat insulation layer is obtained by removing the adhesive and cleaning.

[0038] Optional, such as Figure 4 The schematic cross-sectional view of the insulation layer shown, and Figure 8 The diagram shows a longitudinal section of the phase-change radio frequency switch. The heat insulation layer completely isolates the Cr heating electrode and the phase-change layer, thereby preventing a short circuit between the Cr heating electrode and the phase-change layer, which could lead to device failure.

[0039] Optionally, the heat insulation layer 6 can be prepared using magnetron sputtering. The thickness of the heat insulation layer is 50 nm. The insulating medium used in the heat insulation layer is SiO2.

[0040] Step 103: After aligning the cross marks on the upper surface of the heat insulation layer with electron beam lithography and patterning, a 100nm thick Ge-Sb-Te based phase change material is deposited by pulsed laser as a marker for the phase change layer and the next layer. The phase change layer is then obtained by removing the resist and cleaning.

[0041] Optional, such as Figure 5 The schematic cross-sectional view of the phase change layer shown is as follows: Figure 8 The diagram shows a longitudinal section of a phase-change radio frequency switch, with the phase-change layer located above the thermal insulation layer.

[0042] Optionally, the Ge-Sb-Te based phase change material is GeTe phase change material, and the thickness of the phase change layer is 100 nm. The pulsed laser deposition parameters are set as follows: laser frequency of 5 Hz, TS distance of 5.5 cm, deposition pressure of 2 Pa, and deposition temperature of room temperature.

[0043] Step 104: After aligning the cross marks on the upper surface of the phase change layer with electron beam lithography and patterning, Cr-Au is thermally evaporated and deposited as a radio frequency transmission layer, wherein the thickness of the Cr layer is 7nm and the thickness of the Au layer is 100nm. After removing the resist and cleaning, the radio frequency transmission layer is obtained.

[0044] like Figure 6 The schematic diagram of the cross-section of the radio frequency transmission electrode shown shows that the thickness of the Cr layer in the Cr-Au radio frequency transmission layer is 7nm, the thickness of the Au layer (T) is 100nm, and the design impedance is generally 50 Ω.

[0045] Step 105: After magnetron sputtering to deposit a 100nm thick silicon nitride or titanium nitride on the upper surface of the phase change layer, electron beam lithography is performed to align the cross marks and pattern the layers. Then, reactive ion etching is used to etch the layers to the radio frequency transmission layer. A 100nm thick Cu layer is then thermally evaporated to deposit as the radio frequency transmission electrode pressure contact. The resist is removed and the layers are cleaned to obtain the passivation layer.

[0046] like Figure 7 The diagram shows a cross-sectional view of the passivation layer and the RF transmission electrode pressure contact, wherein the area of ​​the RF transmission electrode pressure contact is 50 μm * 50 μm.

[0047] Step 106: After protecting the upper surface with epoxy resin or paraffin, perform chemical mechanical polishing on the lower surface of the substrate to thin the Si substrate to a maximum of 100 μm.

[0048] Step 107: Based on the cross mark on the upper surface of the passivation layer, after aligning with the double-sided alignment process, the lower surface of the substrate is patterned by ultraviolet photolithography. Then, the lower surface of the substrate is etched through to the heating electrode pressure contact to obtain a silicon via. After that, metal material is electroplated to fill the silicon via, the resist is removed and cleaned, and Au metal contacts are ultrasonically spot-welded at the back via to obtain a low parasitic capacitance phase change RF switch based on the heater's non-plane structure.

[0049] like Figure 8 The schematic diagram of the longitudinal section of the phase change radio frequency switch shows that a complete low parasitic capacitance phase change radio frequency switch based on a heater-based non-surface structure consists of the following components from bottom to top: Au lower surface contact point 1, Cu-filled silicon via 2, high-resistivity single crystal Si substrate 3, SiO2 layer 4, Cr heating electrode 5, SiO2 heat insulation layer 6, GeTe phase change layer 7, Cr-Au radio frequency transmission layer 8, silicon nitride passivation layer 9, and radio frequency transmission electrode pressure contact 10.

[0050] like Figure 9A perspective view of a low parasitic capacitance phase-change RF switch based on a heater-based out-of-plane structure is shown. A complete low parasitic capacitance phase-change RF switch based on a heater-based out-of-plane structure includes: Au lower surface contact points as electrical pulse input / output ports 1a / 1b, Cu-filled silicon vias as electrical pulse input / output paths 2a / 2b, a high-resistivity single-crystal Si substrate 3, a SiO2 layer on the silicon substrate 4, a Cr heating electrode 5, a SiO2 thermal insulation layer 6, a GeTe phase-change layer 7, RF input / output electrodes 8a / 8b, a silicon nitride passivation layer 9, RF input / output electrode pressure contacts 10a / 10b, and RF input / output ports 11a / 11b.

[0051] like Figure 10 The simulation comparison of insertion loss performance of the phase-change RF switch with low parasitic capacitance based on heater-out-of-plane structure and phase-change RF switch with coplanar structure in the DC-40GHz frequency range is shown in the figure. The insertion loss of the phase-change RF switch with coplanar structure in the heater reaches 0.675dB at 40GHz, while the insertion loss of the phase-change RF switch with low parasitic capacitance based on heater-out-of-plane structure of the present invention is only 0.555dB at 40GHz, which is a reduction of 0.12dB.

[0052] The greatest advantage of this invention compared to existing technologies lies in the fact that the phase-change radio frequency switch in this embodiment is manufactured using mature silicon semiconductor processes. The device is heated via an embedded indirect heating method, utilizing through-silicon via (TSV) technology to position the heating element's terminal circuit at a different level relative to the phase-change material layer and the radio frequency transmission layer. This does not increase manufacturing complexity or device size, and parasitic capacitance is significantly reduced. In this embodiment, the parasitic capacitance of the radio frequency phase-change switch is approximately 100 angstroms, which is negligible.

[0053] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the above embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for fabricating a low parasitic capacitance phase-change radio frequency switch based on a heater-based non-planar structure, characterized in that, The method includes the following specific steps: Step 1: Select a single-sided oxidized high-resistivity single crystal Si as the substrate. After cleaning, it is patterned by electron beam lithography. Then, a channel with a depth of 200-500 nm is etched by reactive ion etching. Immediately afterwards, a Cr or W metal heating electrode with a thickness of 200-500 nm and the markings for the next layer are deposited by electron beam evaporation. This ensures that the depth of the channel and the thickness of the heating electrode are the same. The elongated part of the heating electrode is the heating area, with a specific size of 0.5-1 μm in width and 5-20 μm in length. The heating layer is obtained by removing the resist and cleaning. Step 2: A 50-200 nm thick SiO2 or Ta2O5 heat insulation layer is deposited on the upper surface of the heating layer by magnetron sputtering, and the heat insulation layer is obtained by removing the adhesive and cleaning. Step 3: After electron beam lithography patterning on the upper surface of the heat insulation layer according to the cross mark alignment, a 100-200 nm thick Ge-Sb-Te based phase change material and the next layer of lithographic marks are deposited by pulsed laser. The phase change layer is obtained by removing the resist and cleaning. Step 4: After electron beam lithography patterning on the upper surface of the phase change layer according to the cross mark alignment, Cr-Au is thermally evaporated and deposited as the radio frequency transmission layer. The thickness of the Cr layer is 7-20 nm, which is used to increase the adhesion of the electrode. The thickness of the Au layer is 100-200 nm. After removing the resist and cleaning, the radio frequency transmission layer is obtained. Step 5: After magnetron sputtering to deposit a 50-200 nm thick silicon nitride or titanium nitride layer on the surface of the phase change layer, electron beam lithography is performed to align the cross marks and pattern the layer. Then, reactive ion etching is used to etch the layer to the radio frequency transmission layer. A 50-200 nm thick Cu layer is thermally evaporated and deposited as the radio frequency transmission electrode pressure contact. The resist is removed and the layer is cleaned to obtain the passivation layer. Step 6: After protecting the upper surface of the passivation layer with epoxy resin or paraffin, perform chemical mechanical polishing on the lower surface of the substrate to thin the Si substrate to a maximum of 150 μm. Step 7: Based on the cross mark on the upper surface of the passivation layer, after aligning with the double-sided alignment process, the lower surface of the substrate is patterned by ultraviolet photolithography. Then, the lower surface of the substrate is etched through to the heating electrode pressure contact to obtain a silicon via. After that, the silicon via is filled by electroplating metal material, the resist is removed and cleaned, and Au metal contacts are ultrasonically spot-welded at the back via to obtain a low parasitic capacitance phase change RF switch based on the heater non-plane structure.

2. The method for fabricating a phase-change radio frequency switch as described in claim 1, characterized in that, The high-resistivity single-crystal Si is used as the substrate, with a resistivity of at least 10000 Ω·cm and a surface SiO2 thickness of at least 100 nm.

3. The method for fabricating a phase-change radio frequency switch as described in claim 1, characterized in that, The contact area between the through-silicon via and the heating electrode is at least 10 μm * 10 μm.

4. The method for fabricating a phase-change radio frequency switch as described in claim 1, characterized in that, The Ge-Sb-Te based phase change material is Ge2Sb2Te5, Sb2Te3, Sb2Te, GeSb2Te4, or GeTe.

5. The method for fabricating a phase-change radio frequency switch as described in claim 1, characterized in that, The area of ​​the pressure contact point of the upper surface radio frequency transmission electrode is at least 50 μm*50 μm.

6. The method for fabricating a phase-change radio frequency switch as described in claim 1, characterized in that, The area of ​​the Au metal contact at the through hole on the back is at least 50 μm*50 μm.

7. The method for fabricating a phase-change radio frequency switch as described in claim 1, characterized in that, The metal material used to fill the through-silicon via is Cu.

8. A low parasitic capacitance phase-change radio frequency switch based on a heater-plane structure, fabricated by the method of claim 1.

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