An EWOD chip structure based on GaN-based switch

Abstract

The application discloses an EWOD chip structure based on GaN-based switches, which comprises a substrate and an upper plate, the substrate comprises at least two GaN-based switches, and each GaN-based switch is located in the same height plane; the GaN-based switch is provided with a substrate, a GaN layer is epitaxially grown on the substrate, an AlGaN layer is arranged above the GaN layer, and a two-dimensional electron gas is formed between the GaN layer and the AlGaN layer; the AlGaN layer is respectively provided with an ohmic-contact source electrode and a drain electrode, a recess is arranged on the upper surface of the AlGaN layer, and a gate electrode is deposited in the recess; each drain electrode is electrically connected with a metal electrode on one side; the source electrode, the drain electrode, the gate electrode and the metal electrode are provided with an insulating layer for insulation protection; the outer surface of the insulating layer is respectively provided with an electrically-conductive channel reaching the source electrode, the drain electrode and the gate electrode; and a hydrophobic layer is arranged above the insulating layer; through the integrated treatment of the GaN-based switch and the metal electrode, the occupied space of the external circuit and the switch is saved, the volume and the weight of the entire EWOD system are reduced, and the application range of the EWOD chip is enlarged.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology, and particularly relates to an EWOD chip structure based on GaN-based switches. Background Technology

[0002] Digital microfluidics is a technology that manipulates tiny droplets on a chip. EWOD (Electronic Waveform Discharge) is one such technique, which drives droplets by applying voltage to electrodes to change the droplet's contact angle. Specifically, when a voltage is applied to one electrode, the droplet's contact angle changes according to the Lippmann-Young equation, while on the other side, where there is no voltage, the droplet's contact angle remains unchanged. Figure 1 As shown, the different contact angles on both sides of the droplet create a pressure difference within it, driving the droplet's movement. When voltage is applied to a series of electrodes in a specific sequence, the droplet can move along a predetermined path. In practice, the EWOD chip has several individual electrodes, and each electrode is equipped with a separate switch outside the EWOD chip. An external circuit is connected between the individually configured switch and the electrode. The voltage on each electrode is controlled by the switch, thereby changing the contact angle of the droplet and driving it, thus realizing the function of the EWOD chip. However, the inventors believe that the individually configured switch undoubtedly requires additional space, increasing the size and weight of the EWOD chip structure. Therefore, it is necessary to design an EWOD chip structure based on a GaN-based switch.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art. Summary of the Invention

[0004] The inventors discovered through research that, due to the operating conditions of the EWOD chip structure, a switch is needed to change the voltage on the electrodes. The separate setting of the switch requires a dedicated space for its placement, which undoubtedly increases the size and weight of the entire EWOD chip system, thereby reducing the applicable scope of the EWOD chip structure.

[0005] In view of at least one of the above-mentioned technical problems, this disclosure provides an EWOD chip structure based on GaN-based switches, and the specific technical solution is as follows:

[0006] An EWOD chip structure based on GaN-based switches includes a substrate and a top plate. The substrate includes at least two GaN-based switches, each located on the same height plane. Each GaN-based switch has a substrate on which a GaN layer is epitaxially grown. An AlGaN layer is disposed above the GaN layer, forming a two-dimensional electron gas between the GaN and AlGaN layers. The AlGaN layer has ohmic contact source and drain electrodes, respectively. A groove is formed on the upper surface of the AlGaN layer, and a gate electrode is deposited within the groove. Each drain electrode is electrically connected to a metal electrode on one side. An insulating layer is provided to protect the source, drain, gate, and metal electrode. A conductive path to the source, drain, and gate electrodes is provided on the outer surface of the insulating layer. A hydrophobic layer is disposed above the insulating layer. By integrating the GaN-based switches with the metal electrodes, the space occupied by external circuitry and the switches is saved, reducing the size and weight of the entire EWOD system and expanding the applicability of the EWOD chip.

[0007] In some embodiments of this disclosure, the source, drain, and gate are each electrically connected to a power supply device in their respective power supply channels.

[0008] In some embodiments of this disclosure, the upper end of the gate is higher than the upper end of the source; the upper ends of the corresponding lead-in devices of the source, drain and gate are at the same height.

[0009] In some embodiments of this disclosure, the power supply device is a cap-post structure.

[0010] In some embodiments of this disclosure, the insulating layer includes a first insulating layer, a second insulating layer, and a third insulating layer; the first insulating layer covers the source and drain, the second insulating layer covers the gate and the first insulating layer, the metal electrode is located on the second insulating layer, and the third insulating layer covers the metal electrode and the second insulating layer.

[0011] In some embodiments of this disclosure, the substrate is a silicon substrate, a silicon carbide substrate, or a sapphire substrate.

[0012] In some embodiments of this disclosure, the metal electrodes are rectangular, and the adjacent sides of each metal electrode are parallel to each other.

[0013] In some embodiments of this disclosure, the metal electrodes are arranged at equal intervals.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. By integrating GaN-based switches with metal electrodes, the space occupied by external circuits and switches is saved, reducing the size and weight of the entire EWOD system, making its structure more streamlined, and expanding the application range of EWOD chips.

[0016] 2. After the device is fabricated, the change in the contact angle of the droplet is proportional to the applied voltage V. Since GaN HEMT devices have the advantage of high voltage resistance, the circuit can withstand a larger voltage, thereby obtaining a larger contact angle change and making the droplet driving effect better.

[0017] 3. Because GaN HEMT devices are resistant to high temperatures, GaN-based EWOD chips can be used in environments with higher temperatures.

[0018] 4. GaN devices, with their high switching speed and low on-resistance, are more suitable for high-frequency, high-efficiency, and high-power-density applications. Since the speed of droplet movement is related to the frequency of circuit switching, this structure can achieve a faster droplet movement speed, thereby saving the time of droplet movement. Attached Figure Description

[0019] Figure 1 A schematic diagram of an EWOD chip driving a droplet;

[0020] Figure 2 This is a schematic diagram of the GaN-based EWOD chip structure in this invention;

[0021] Figure 3 This is a schematic diagram of the source, drain, and gate of the EWOD chip structure in Embodiment 1 of the present invention;

[0022] Figure 4 This is a schematic diagram of the EWOD system in this invention.

[0023] The following are the labels in the diagram: 1. Substrate; 11. GaN-based switch; 111. Substrate; 112. GaN layer; 113. AlGaN layer; 114. Two-dimensional electron gas; 12. Source; 13. Drain; 14. Gate; 2. Top plate; 3. Metal electrode; 4. Insulating layer; 41. First insulating layer; 42. Second insulating layer; 43. Third insulating layer; 5. Hydrophobic layer; 6. Power supply; 7. Controller; 8. External circuitry. Detailed implementation method:

[0024] To better understand the purpose, structure, and function of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0025] The component numbers used in this document are solely for distinguishing the objects described and have no sequential or technical meaning. The term "connection" in this disclosure, unless otherwise specified, includes both direct and indirect connections. In the description of this application, it should be understood that directional terms such as "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and for a brief description, and do not indicate or imply that the device or unit referred to must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this application.

[0026] like Figures 1 to 4 As shown, an EWOD chip structure based on GaN-based switches is designed. This structure is a bipolar plate structure, including a substrate 1 and an upper plate 2, with a controlled droplet located between the substrate 1 and the upper plate 2. The substrate 1 includes at least two GaN-based switches 11, each GaN-based switch 11 being located at the same height plane. Each GaN-based switch 11 has a substrate 111, on which a GaN layer 112 is epitaxially grown. An AlGaN layer 113 is located above the GaN layer 112, forming a two-dimensional electron gas 114 between the GaN layer 112 and the AlGaN layer 113. The AlGaN layer 113 has ohmic contact source 12 and drain 13, respectively. The gate 14 is deposited on the upper surface of the N-layer 113 using a grooved gate technique, making the device an enhancement-mode device. Specifically, a groove is provided on the upper surface of the AlGaN layer 113, and the gate 14 is deposited in the groove. When a positive voltage exceeding the threshold voltage is applied to the gate 14, the source 12 and drain 13 are turned on, and vice versa. Each drain 13 is electrically connected to a metal electrode 3 on one side. The source 12, drain 13, gate 14 and metal electrode 3 are provided with an insulating layer 4 for isolation and protection. The outer surface of the insulating layer 4 is provided with a current-carrying channel to the source 12, drain 13 and gate 14. A hydrophobic layer 5 is provided above the insulating layer 4, and the controlled droplet is located on the hydrophobic layer.

[0027] In use, the gate 14 of the GaN-based switch 11 is connected to the controller 7, and the source 12 and drain 13 are connected to the external circuit 8. Depending on the connection method, the GaN-based switch 11 has different control methods.

[0028] If this disclosure defines "on" as the conduction of the GaN-based switch 11, meaning there is a potential difference between a single electrode on the substrate 1 and the upper plate 2, then when a positive voltage is applied to the gate 14 of one side of the GaN-based switch 11 using the controller 7, the circuit is turned on, charge accumulates on the metal electrode 3, and the droplet contact angle changes. Meanwhile, the gate 14 of the other side of the GaN-based switch 11 has no voltage, and the droplet contact angle remains unchanged. Therefore, the droplet moves towards the metal electrode 3 on the side where the conduction is active. If this disclosure defines "on" as the disconnection of the GaN-based switch, meaning there is no potential difference between a single electrode on the substrate 1 and the upper plate 2, then when a positive voltage is applied to the gate 14 of one side of the GaN-based switch 11 using the controller 7, the circuit is disconnected, the droplet contact angle on the metal electrode 3 remains unchanged, while the gate 14 of the other side of the GaN-based switch 11 has no voltage, the circuit is turned on, and the droplet contact angle changes. Therefore, the droplet moves towards the side where the contact angle changes.

[0029] This disclosure uses an enhanced GaN HEMT device as a switch for an EWOD chip and integrates it with the EWOD chip. By controlling the on / off state of the GaN-based switch 11, the droplet can be controlled to move along a certain path.

[0030] like Figure 1 As shown, according to the Lippmann-Young equation Where, θ V θ0 is the contact angle of the droplet when a voltage is applied, θ0 is the contact angle when no voltage is applied, ε0 is the vacuum permittivity, and ε r γ is the relative permittivity of the insulating layer, d is the thickness of the insulating layer, and γ is the relative permittivity of the insulating layer. lg The surface tension of the liquid and gas is given by V, where V is the applied voltage. Therefore, after the device is fabricated, the change in the contact angle of the droplet is proportional to the applied voltage V. Because GaN HEMT devices have the advantage of high voltage resistance, the circuit can withstand higher voltages, resulting in a larger contact angle change and thus better droplet driving performance. Due to the high temperature resistance of GaN HEMT devices, EWOD chips based on GaN-based switches can be used in higher temperature environments. GaN devices, with their high switching speed and low on-resistance, are more suitable for high-frequency, high-efficiency, and high-power-density applications. Since the speed of droplet movement is related to the switching frequency of the circuit, this structure can achieve a faster droplet movement speed, thus saving the time required for droplet movement.

[0031] The above embodiments provide one example of how to implement the above technical solution:

[0032] Example 1

[0033] This embodiment provides an EWOD chip structure based on GaN-based switches. The structure is a bipolar plate structure, including a substrate 1 and an upper plate 2. A controlled droplet is located between the substrate 1 and the upper plate 2. In this embodiment, the substrate 1 includes three GaN-based switches 11, such as... Figure 3 As shown, G represents the source 12, D represents the drain 13, G represents the gate 14, and E represents the metal electrode 3. Similarly, it can be any natural number greater than one to ensure that the controlled droplet can move as needed between different metal electrodes 3. The three GaN-based switches 11 are located on the same height plane. The GaN-based switch 11 has a substrate 111. In this disclosure, the substrate 111 can be a silicon substrate, or similarly, a silicon carbide substrate or a sapphire substrate. A GaN layer 112 is epitaxially grown on the substrate 111, and an AlGaN layer 113 is provided above the GaN layer 112. A two-dimensional electron gas 114 is formed between the GaN layer 112 and the AlGaN layer 113. The AlGaN layer 113 has ohmic contact source 12 and drain 13 respectively. The gate 14 is deposited on the upper surface of the AlGaN layer 113 using a grooved gate technique. 4; thus making the device an enhancement-mode device, when a positive voltage exceeding the threshold voltage is applied to the gate 14, the source 12 and drain 13 conduct, and vice versa; each drain 13 is electrically connected to a metal electrode 3 on one side, the metal electrode 3 is rectangular, and the adjacent sides of each metal electrode 3 are parallel to each other, so that the gap between adjacent metal electrodes is consistent, ensuring that the controlled droplet does not change its moving direction from left to right; it can move better according to the designed direction; the metal electrodes 3 are arranged at equal intervals to ensure the smoothness of the controlled droplet movement; the source 12, drain 13, gate 14 and metal electrode 3 are provided with an insulating layer 4 for isolation and protection; the outer surface of the insulating layer 4 is provided with a power-leading channel leading to the source 12, drain 13 and gate 14 respectively; the source 12, drain 13 and gate 14 are electrically connected to a power-leading device in their respective power-leading channels; such as Figure 2As shown, the upper end of the gate 14 is higher than the upper end of the source 12, and the upper ends of the source 12 and the drain 13 are at the same height. The upper ends of the corresponding lead-in devices of the source 12, drain 13 and gate 14 are at the same height, which facilitates overall packaging and results in good flatness and an aesthetically pleasing appearance. The lead-in device is a cap-post structure, and the lower end of the lead-in device is electrically connected to the source 12, drain 13 or gate 14 of the corresponding GaN-based switch 11. The insulating layer 4 includes a first insulating layer 41, a second insulating layer 42 and a third insulating layer 43. The first insulating layer 41 covers the source 12 and drain 13 and is used to passivate the GaN HEMT device to prevent current collapse. The second insulating layer 42 covers the gate 14 and the first insulating layer 41 and is used to protect the gate 14. The metal electrode 3 is located on the second insulating layer 42. The third insulating layer 43 covers the metal electrode 3 and the second insulating layer 42 to allow charge to accumulate on the electrode. A hydrophobic layer 5 is provided above the insulating layer 4, and the controlled droplet is located on the hydrophobic layer.

[0034] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. An EWOD chip structure based on GaN-based switches, comprising a substrate (1) and a top plate (2), characterized in that, The substrate (1) includes at least two GaN-based switches (11), each GaN-based switch (11) being located at the same height plane; the GaN-based switch (11) is provided with a substrate (111), on which a GaN layer (112) is epitaxially grown, and an AlGaN layer (113) is provided above the GaN layer (112), forming a two-dimensional electron gas (114) between the GaN layer (112) and the AlGaN layer (113); the AlGaN layer (113) is provided with a source (12) and a drain (13) with ohmic contacts, and a groove is provided on the upper surface of the AlGaN layer (113), in which a gate (14) is deposited; each drain The electrode (13) is electrically connected to a metal electrode (3) on one side. The metal electrode (3) is rectangular. The adjacent sides of each metal electrode (3) are parallel to each other, so that the gaps between adjacent metal electrodes (3) are consistent, ensuring that the controlled droplet will not change its direction of movement from left to right. The metal electrodes (3) are arranged at equal intervals to ensure the smooth movement of the controlled droplet. The source electrode (12), drain electrode (13), gate electrode (14) and metal electrode (3) are provided with an insulating layer (4) for isolation and protection. The outer surface of the insulating layer (4) is provided with a power-leading channel that leads to the source electrode (12), drain electrode (13) and gate electrode (14). A hydrophobic layer (5) is provided above the insulating layer (4).

2. The EWOD chip structure based on GaN-based switches according to claim 1, characterized in that, The source (12), drain (13) and gate (14) are each electrically connected to a power supply device in their respective power supply channels.

3. The EWOD chip structure based on GaN-based switches according to claim 2, characterized in that, The upper end of the gate (14) is higher than the upper end of the source (12); the upper ends of the corresponding power supply devices of the source (12), drain (13) and gate (14) are at the same height.

4. The EWOD chip structure based on GaN-based switches according to claim 3, characterized in that, The power supply device is a cap-post structure.

5. The EWOD chip structure based on GaN-based switches according to claim 3, characterized in that, The insulating layer (4) includes a first insulating layer (41), a second insulating layer (42) and a third insulating layer (43); the first insulating layer (41) covers the source (12) and the drain (13), the second insulating layer (42) covers the gate (14) and the first insulating layer (41), the metal electrode (3) is located on the second insulating layer (42), and the third insulating layer (43) covers the metal electrode (3) and the second insulating layer (42).

6. The EWOD chip structure based on GaN-based switches according to claim 1, characterized in that, The substrate (111) is a silicon substrate, a silicon carbide substrate, or a sapphire substrate.

7. The EWOD chip structure based on GaN-based switches according to claim 1, characterized in that, The metal electrode (3) is rectangular, and the adjacent sides of each metal electrode (3) are parallel to each other.

8. The EWOD chip structure based on GaN-based switches according to claim 1, characterized in that, The metal electrodes (3) are arranged at equal intervals.

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