CN105048999B - Gallium nitride base low-leakage current double cantilever beam switchs the rest-set flip-flop of nor gate - Google Patents

Abstract

The GaN-based RS flip-flop with dual cantilever switch NOR gates of the present invention replaces conventional NOR gates with MESFET NOR gates having dual cantilever beam switches, the positions of the two cantilever beam switches are relative to the MESFET source- The drain direction is symmetrical, a Schottky contact is formed between the gate of the MESFET and the substrate, and a depletion layer is formed in the substrate below the gate, and the pull-down voltage of the cantilever switch is designed to be equal to the threshold voltage of the MESFET. When the voltage applied between the cantilever beam switch and the pull-down electrode is greater than the threshold voltage of the MESFET, the cantilever beam pull-down and the gate are close to make the MESFET turn on. When the applied voltage is less than the threshold voltage of the N-type MESFET, the cantilever beam switch cannot pull down, the MESFET is turned off, and when the RS flip-flop is working, the cantilever switch is in a suspended state when the NMESFET is turned off, which reduces the gate leakage current, thereby reducing the power consumption of the RS flip-flop.

Description

GaN-Based Low Leakage Current Double Cantilever Beam Switch NOR Gate RS Flip-Flop

technical field

The invention provides a GaN-based low-leakage current dual cantilever beam switch MESFET RS flip-flop for a NOR gate, which belongs to the technical field of micro-electromechanical systems.

Background technique

With the development of wireless communication technology, the chips of radio frequency integrated circuits are also developing rapidly, the scale of integration continues to expand, and the operating frequency continues to increase. Traditional silicon-based materials can no longer meet the requirements. MESFET based on gallium nitride substrate is proposed and applied under this background. Due to the good characteristics of gallium nitride material, the transistor manufactured by it has high electron mobility, strong radiation resistance, and large range of working temperature. As the number of transistors in a chip increases, so does the power consumption of integrated circuits. With the development of integrated circuits, the scale of chips becomes larger, and people pay more and more attention to the power consumption of chips. Too high power consumption will impose higher requirements on the heat dissipation material of the chip, and will also affect the performance of the chip. Therefore, the design of low power consumption of devices is becoming more and more important in the design of integrated circuits.

As an important part of digital circuits, RS flip-flop circuit is the basic component of various flip-flop circuits with complex functions, and has huge applications. The RS flip-flop composed of conventional MESFET, with the improvement of integration, the power consumption It is becoming more and more serious. The overheating of the chip caused by excessive power consumption will seriously affect the performance of the integrated circuit. The MESFET with a movable cantilever switch structure proposed in this paper can effectively reduce the gate leakage current, thereby reducing the RS flip-flop power consumption of the circuit.

Contents of the invention

Technical problem: the purpose of this invention is to provide a kind of RS flip-flop of GaN-based low leakage current double cantilever switch MESFET NOR gate. Replace the traditional two RS flip-flop circuits of NOR gates composed of conventional MESFETs with two RS flip-flops of MESFET NOR gates with a double cantilever beam switch structure. When the RS flip-flops are in working condition, they can be effectively The gate leakage current of the transistor is greatly reduced, thereby reducing the power consumption of the RS flip-flop.

Technical solution: The RS flip-flop of the gallium nitride-based low leakage current double cantilever switch NOR gate of the present invention is composed of a first N-type MESFET and a second N-type MESFET with a double cantilever switch, a resistor and a power supply. Beam switch The first N-type MESFET and the second N-type MESFET are fabricated on a semi-insulating GaN substrate, and the source and drain of the first N-type MESFET and the second N-type MESFET are formed by metal and heavily doped N regions to form ohmic contacts The gate is composed of titanium/platinum/gold alloy and N-type active layer to form a Schottky contact. Two symmetrically designed cantilever beam switches made of titanium/gold/titanium are suspended above the gate. There is a gap between the floating ends of the two cantilever switches to ensure that the two cantilever switches do not interfere with each other when they are pulled down. The positions of the two cantilever switches are symmetrical with respect to the source-drain direction of the MESFET. On the insulating GaN substrate, there is a pull-down electrode between the cantilever beam switch and the substrate, the pull-down electrode is covered by silicon nitride material, the pull-down electrode and the source are grounded, the drain is connected to the power supply VCC through a resistor, the source and drain The wires connected on the top are made of gold; in the first N-type MESFET and the second N-type MESFET of the RS flip-flop, there is a cantilever switch respectively as the input terminals S and R of the RS flip-flop, and the output terminal Q is in the double Cantilever switch output between the drain of the second N-type MESFET and the resistor, output Output between the drain of the first N-type MESFET and the resistor, another cantilever switch of the first N-type MESFET is connected to the drain of the second N-type MESFET through a lead, and the other cantilever of the second N-type MESFET is also The switch is connected to the drain of the first N-type MESFET through a lead wire to form a symmetrical structure. In order to ensure that when the first N-type MESFET and the second N-type MESFET of the double cantilever beam switch are turned on, the output obtained by dividing the voltage by the resistor is a low voltage. flat, the resistance value of the resistor is much larger than the conduction resistance of the first N-type MESFET and the second N-type MESFET.

The cantilever switch is suspended above the gate by the support of the anchor region, and a Schottky contact is formed between the gate and the substrate; the two cantilever switches of the first N-type MESFET and the second N-type MESFET The pull-down voltage is designed to be equal to the threshold voltage of the N-type MESFET. Only when the voltage applied to the cantilever switch of the N-type MESFET is greater than the threshold voltage of the N-type MESFET, the cantilever switch can be pulled down and contact the gate. Therefore, the double cantilever beam switch MESFET is turned on. When the applied voltage is less than the threshold voltage of the double cantilever beam switch MESFET, the cantilever beam switch cannot be pulled down, and the double cantilever beam switch MESFET is turned off. When the RS flip-flop is working, when the double cantilever beam switch When the switch MESFET is turned off, its cantilever beam switch is in a suspended state, which reduces the gate leakage current, thereby reducing the power consumption of the circuit.

When the RS flip-flop is in the working state, define Q=1, For the 1 state of the flip-flop, define Q=0, It is the 0 state of the flip-flop, S is called the set terminal, and R is called the reset terminal. When S=1, R=0, since the input terminal S is connected to a high level, the cantilever beam switch corresponding to the input terminal S is pulled down and the first N-type MESFET of the double cantilever beam switch is turned on to output is low level, that is Q=1, after the S=1 signal disappears, because the high level of the Q terminal is connected back to the double cantilever switch of the RS flip-flop and the other cantilever switch of the first N-type MESFET is pulled down, so that the output Maintained at low level, so the 1 state of the circuit is maintained; when S=0, R=1, since the input terminal R is connected to high level, the cantilever beam switch corresponding to the input terminal R pulls down and makes the double cantilever beam switch second The N-type MESFET is turned on so that the output Q is low, that is, Q=0, After the R=1 signal disappears, the 0 state of the circuit remains unchanged; when S=R=0, the circuit maintains the original state; when S=R=1, This state is not allowed and is a constraint of the RS flip-flop. The state of the N-type MESFET in the flip-flop also changes between on and off as the input signal changes. When the N-type MESFET is in the off state, its cantilever beam switch is in a suspended state, which reduces the gate leakage current. , thereby reducing the power consumption of the RS flip-flop. Since the second state Q ⁿ⁺¹ of the RS flip-flop is not only related to the input state, but also related to the original state Q (also called the initial state) of the RS flip-flop, the truth table of the obtained RS flip-flop is as follows:

S R Q Q ⁿ⁺¹ 0 0 0 0 0 0 1 1 1 0 0 1 1 0 1 1 0 1 0 0 0 1 1 0

Beneficial effects: when the two cantilever switches of the GaN-based low-leakage current double cantilever switch MESFET in the RS flip-flop of the NOR gate of the present invention are in contact with the gate of the N-type MESFET, the N-type MESFET turns on. When the voltage applied between the cantilever switch and the pull-down electrode is less than the threshold voltage of the MESFET, the cantilever switch cannot be pulled down, and the N-type MESFET is turned off. At this time, the cantilever switch is in a floating state, which reduces the gate leakage current and thus reduces the Power consumption of the RS flip-flop.

Description of drawings

Fig. 1 is the top view of the RS flip-flop of the GaN-based low leakage current double cantilever switch MESFET NOR gate of the present invention,

Figure 2 is a cross-sectional view of the P-P' direction of the RS flip-flop of the GaN-based low-leakage current double cantilever switch MESFET NOR gate in Figure 1,

Fig. 3 is an A-A' cross-sectional view of the RS flip-flop of the GaN-based low-leakage current double cantilever switch MESFET NOR gate in Fig. 1 .

The figure includes: a first N-type MESFET1, a second switch N-type MESFET2, a semi-insulating GaN substrate 3, a lead 4, a gate 5, a cantilever beam switch 6, an anchor region 7, a pull-down electrode plate 8, and a silicon nitride layer 9 , source 10, N-type active layer 11, drain 12, resistor 13.

detailed description

The RS flip-flop of the GaN-based low-leakage current double cantilever switch MESFET NOR gate of the present invention is composed of two double cantilever switch N-type MESFETs, that is, the first N-type MESFET1, the second switch N-type MESFET2, and a resistor 13. The source 10 and drain 12 of the MESFET are composed of metal and heavily doped N regions to form ohmic contacts, and the gate 5 is composed of titanium/platinum/gold alloy and N-type active layer 12 to form Schottky contacts. Two symmetrically designed cantilever beam switches 6 made of titanium/gold/titanium are suspended above the gate 5 of the switching N-type MESFET. A certain gap is left at the suspension ends of the two cantilever beam switches 6 to ensure that the two cantilever beams The switch 6 does not interfere with each other when pulled down, and the positions of the two cantilever beam switches 6 are symmetrical with respect to the source-drain direction of the N-type MESFET. The anchor region 7 of the cantilever switch 6 is made on the semi-insulating GaN substrate 3, and there is a pull-down electrode 8 between the cantilever switch 6 and the substrate, and the pull-down electrode 8 is covered by a silicon nitride material 9, and the cantilever switch N-type MESFET The pull-down electrode 8 is grounded. The first N-type MESFET1 and the second N-type MESFET2 of the dual cantilever switch of the RS flip-flop each have a cantilever switch as the input terminals S and R of the RS flip-flop, and the output terminal Q is at the first of the double cantilever switch. Output between the drain of N-type MESFET1 and the resistor, the output Output between the drain of the first N-type MESFET1 of the double cantilever beam switch and the resistor, the sources of the first N-type MESFET1 and the second N-type MESFET2 are both grounded, and the other cantilever switch of the first N-type MESFET1 connects with the lead wire The drain of the second N-type MESFET 2 of the double cantilever switch is connected, and the other cantilever switch of the second N-type MESFET 2 of the double cantilever switch is connected with the drain of the first N-type MESFET 1 of the double cantilever switch through a lead wire, forming a symmetrical In order to ensure that when the MESFET is turned on, the output obtained by dividing the voltage by the resistor is a low level, the resistance value of the resistor 13 is much larger than the impedance of the MESFET turned on.

When the RS flip-flop is in the working state, define Q=1, For the 1 state of the flip-flop, define Q=0, It is the 0 state of the flip-flop, S is called the set terminal, and R is called the reset terminal. When S=1, R=0, since the input terminal S is connected to a high level, the cantilever beam switch corresponding to the input terminal S is pulled down and the first N-type MESFET 1 of the double cantilever beam switch is turned on to output is low level, that is Q=1, after the S=1 signal disappears, because the high level of the Q terminal is connected back to another cantilever switch of the first N-type MESFET 1 of the double cantilever switch and makes it pull down, so that the output is low level, so the 1 state of the circuit is maintained; when S=0, R=1, since the input terminal R is connected to a high level, the cantilever beam switch corresponding to the input terminal R is pulled down and the double cantilever beam switch second N The type MESFET2 is turned on so that the output Q is low level, that is, Q=0, After the R=1 signal disappears, the 0 state of the circuit remains unchanged; when S=R=0, the circuit maintains the original state; when S=R=1, This state is not allowed and is a constraint of the RS flip-flop. The state of the N-type MESFET in the flip-flop also changes between on and off as the input signal changes. When the N-type MESFET is in the off state, its cantilever beam switch is in a suspended state, which reduces the gate leakage current. , thereby reducing the power consumption of the RS flip-flop.

The preparation method of the RS flip-flop of the GaN-based low-leakage current double cantilever switch MESFET NOR gate includes the following steps:

1) Prepare a semi-insulating GaN substrate;

2) Deposit silicon nitride, grow a layer of silicon nitride by plasma enhanced chemical vapor deposition (PECVD), and then photolithography and etch silicon nitride to remove silicon nitride in the active area of N-type MESFET ;

3) Ion implantation in the active area of N-type MESFET: after implanting phosphorus, anneal in nitrogen environment; after annealing, redistribute N ⁺ impurities at high temperature to form the N-type active layer in the active area of N-type MESFET;

4) Removing the silicon nitride layer: using dry etching technology to remove all the silicon nitride;

5) photolithography switch area, removing the photoresist in the switch area;

6) Electron beam evaporation of titanium/platinum/gold;

7) removing the photoresist and the titanium/platinum/gold on the photoresist;

8) heating to form a Schottky contact between the titanium/platinum/gold alloy and the N-type GaN active layer;

9) Coating photoresist, photolithography and etching the photoresist in the source and drain regions of the N-type MESFET;

10) Implanting heavily doped N-type impurities, forming N-type heavily doped regions in the N-type MESFET source and drain regions, and performing rapid annealing after implantation;

11) Photoetching the source and drain, removing the photoresist of the leads, source and drain;

12) Vacuum evaporation of gold germanium nickel/gold;

13) remove the photoresist and the gold germanium nickel/gold on the photoresist;

14) Alloying to form ohmic contact, forming leads, source and drain;

15) Coating photoresist, removing the photoresist at the anchor area position of the input lead, the electrode plate and the fixed support beam;

16) Evaporate the first layer of gold with a thickness of about 0.3 μm;

17) Remove the photoresist and the gold on the photoresist, and initially form the anchor area of the input lead, the electrode plate and the fixed support beam;

18) Deposition of silicon nitride: growth by plasma-enhanced chemical vapor deposition (PECVD) Thick silicon nitride dielectric layer;

19) Photolithography and etching the silicon nitride dielectric layer, and the silicon nitride on the electrode plate is retained;

20) Deposit and lithography polyimide sacrificial layer: Coat a 1.6 μm thick polyimide sacrificial layer on the gallium arsenide substrate, and it is required to fill the pits; photolithography polyimide sacrificial layer, only Retain the sacrificial layer under the fixed beam;

21) Evaporate titanium/gold/titanium with a thickness of 500/1500/ Evaporation of base gold for electroplating;

22) Photolithography: remove the photoresist at the place to be electroplated;

23) Gold electroplating, the thickness of which is 2 μm;

24) Remove photoresist: remove photoresist where electroplating is not required;

25) Anti-etch titanium/gold/titanium, corrode the bottom gold, and form a solid support beam;

26) Release the polyimide sacrificial layer: soak in developer solution, remove the polyimide sacrificial layer under the fixed beam, soak in deionized water for a while, dehydrate with absolute ethanol, volatilize at room temperature, and dry in the air.

The difference between the present invention and prior art is:

The two cantilever switches of the double cantilever beam switch MESFET used in the RS flip-flop in the present invention are suspended above its grid, and a Schottky contact is formed between the grid of the N-type MESFET and the substrate, and the A depletion layer is formed in the substrate below the gate. The pull-down voltage of the cantilever switch of the N-type MESFET is designed to be equal to the threshold voltage of the MESFET. When the voltage loaded between the cantilever switch and the pull-down electrode is greater than the threshold voltage of the MESFET When the cantilever beam switch is pulled down and close to the gate, the N-type MESFET is turned on. When the voltage applied between the cantilever switch and the pull-down electrode is less than the threshold voltage of the MESFET, the cantilever switch cannot be pulled down, and its MESFET is turned off. At this time, the cantilever switch is in a floating state, which reduces the gate leakage current and thus reduces the RS. power consumption of the flip-flop.

The structure meeting the above conditions is regarded as the RS flip-flop of the GaN-based low leakage current double cantilever switch MESFET NOR gate of the present invention.

Claims (1)

1. A GaN-based RS flip-flop with low leakage current double cantilever beam switch NOR gate is characterized in that the RS flip-flop is composed of a first N-type MESFET (1) and a second N-type MESFET with double cantilever beam switches (2), composed of a resistor (13) and a power supply, the first N-type MESFET (1) and the second N-type MESFET (2) of the double cantilever switch are fabricated on a semi-insulating GaN substrate (3), and the first N-type The source (10) and drain (12) of the MESFET (1) and the second N-type MESFET (2) are made of metal and heavily doped N regions to form ohmic contacts, and the gate (5) is made of titanium/platinum/gold alloy It forms a Schottky contact with the N-type active layer (11), and two symmetrically designed cantilever beam switches (6) made of titanium/gold/titanium are suspended above the gate (5). There is a gap between the floating ends of the beam switch (6) to ensure that the two cantilever beam switches (6) do not interfere with each other when they are pulled down. The positions of the two cantilever beam switches (6) are symmetrical about the source-drain direction of the MESFET. The anchor region (7) of (6) is fabricated on the semi-insulating GaN substrate (3), and a pull-down electrode (8) is arranged between the cantilever beam switch (6) and the substrate, and the pull-down electrode (8) is made of silicon nitride The material (9) covers, the pull-down electrode (8) and the source (10) are grounded, the drain (12) is connected to the power supply VCC through a resistor (13), and the lead ( 4) Made of gold; in the first N-type MESFET (1) and the second N-type MESFET (2) of the RS flip-flop, a cantilever switch (6) is respectively used as the input terminals S and R, the output terminal Q is output between the drain (12) and the resistor of the second N-type MESFET (2) of the double cantilever beam switch, the output terminal Output between the drain (12) of the first N-type MESFET (1) and the resistor, another cantilever switch of the first N-type MESFET (1) is connected to the drain of the second N-type MESFET (2) through a lead Similarly, another cantilever switch of the second N-type MESFET (2) is connected to the drain of the first N-type MESFET (1) through a lead wire to form a symmetrical structure. In order to ensure that when the double cantilever switch first N-type MESFET ( When 1) and the second N-type MESFET (2) are turned on, the output is a low level obtained by dividing the voltage by the resistor, and the resistance value of the resistor (13) is much larger than that of the first N-type MESFET (1) and the second N-type MESFET ( 2) Conduction impedance; The cantilever beam switch (6) is suspended above the gate (5) by relying on the support of the anchor region (7), and a Schottky contact is formed between the gate (5) and the substrate (3); the first N-type MESFET (1) and the pull-down voltages of the two cantilever switches (6) of the second N-type MESFET (2) are designed to be equal to the threshold voltages of the first N-type MESFET (1) and the second N-type MESFET (2), Only when the voltage applied to the cantilever switch (6) of the first N-type MESFET (1) and the second N-type MESFET (2) is greater than that of the first N-type MESFET (1) and the second N-type MESFET (2) ) threshold voltage, the cantilever beam switch (6) can pull down and contact the gate (5) so that the dual cantilever beam switch MESFET is turned on, and when the applied voltage is less than the threshold voltage of the dual cantilever beam switch MESFET, the cantilever beam switch (6) It cannot be pulled down, and the double cantilever switch MESFET is turned off. When the RS flip-flop is working, when the double cantilever switch MESFET is turned off, its cantilever switch (6) is in a floating state, which reduces the gate leakage current, thereby The power consumption of the circuit is reduced.