CN103985608B - MEMS capacitive switch with PN junction - Google Patents

Abstract

An MEMS capacitive switch with PN junction belongs to the technical field of electronics. According to the MEMS capacitive switch, a longitudinal PN junction structure is additionally arranged between an upper driving electrode and a lower driving electrode of the MEMS capacitive switch, when the switch is in an Up state, driving voltage is not applied between the upper driving electrode and the lower driving electrode, and an electric contact point is not contacted with a signal line; when the switch is in a Down state, the upper driving electrode is pulled Down under the action of driving voltage, the electric contact point is contacted with the signal line, and meanwhile, the longitudinal semiconductor PN junction is in a reverse bias state. The MEMS capacitive switch with the PN junction provided by the invention can not generate charge injection and accumulation phenomena when working in a Down state, avoids the problem of bonding failure of an upper driving electrode and a lower driving electrode, and can work under enough driving voltage, so that the close contact between an electric contact point and a signal line can be ensured, and the reliability and the stability of the MEMS capacitive switch can be finally improved.

Description

A MEMS capacitive switch with PN junction

technical field

The invention belongs to the field of electronic science and technology, relates to microelectromechanical systems (MEMS) and semiconductor technology, and specifically refers to a MEMS capacitance switch with a PN junction.

technical background

Switches are fundamental components in radio frequency (RF) and microwave communication systems, and radio frequency microelectromechanical (RF MEMS) switches have great application space at both the RF and microwave component and system levels. At the component level, radio frequency microelectromechanical (RF MEMS) switches can be used to construct voltage-controlled oscillators, filters (capacitive switches, inductors) and phase shifters, etc., which are indispensable components of modern radar and communication systems. Compared with traditional FET and PIN diode switches, radio frequency microelectromechanical (RF MEMS) switches have the characteristics of low DC power consumption, low insertion loss, high isolation, low intermodulation distortion, wide operating frequency band, low cost, and easy integration.

In the existing MEMS capacitive switch, the driving electrode structure of the MEMS capacitor mainly includes two types of contact pull-down structure (as shown in FIG. 1 ) and non-contact pull-down structure (as shown in FIG. 2 ). In the contact pull-down drive electrode structure shown in Figure 1, a layer of insulating dielectric layer 4 (which can be deposited on the surface of any drive electrode) is deposited between the upper and lower drive electrodes, and the DC bias drive voltage is applied between the upper and lower drive electrodes. , the upper and lower drive electrodes generate an electrostatic force, and the electrostatic force pulls down the upper drive electrode 3 (ie, the pull-down drive electrode), so that the electrical contact point 2 on the cantilever beam is in contact with the signal line 7 to generate radio frequency switching characteristics, and the insulating medium layer 4 can be To prevent direct current short circuit caused by direct contact between the upper and lower driving electrodes, the upper driving electrode 3 is pulled down by electrostatic force to form a capacitance with the lower driving electrode 5 and the insulating medium layer 4 . The MEMS capacitive switch with a contact pull-down structure will cause charge injection and accumulation effects in the insulating dielectric layer 4 after long-term application of a DC bias driving voltage, and finally the insulating dielectric layer 4 cannot be released due to excessive charge accumulation, that is, adhesion invalidated. In the non-contact pull-down drive electrode structure shown in Figure 2, after a DC bias drive voltage is applied between the upper and lower drive electrodes, the upper and lower drive electrodes generate electrostatic force, which pulls the upper drive electrode 3 (ie, the pull-down drive electrode) down , so that the electrical contact point 2 on the cantilever beam is in contact with the signal line 7 to produce radio frequency switching characteristics, but when the electrical contact point 2 is in contact with the signal line 7, there is still a certain gap 4' between the upper and lower driving electrodes without direct contact, reaching To avoid the effect of charge injection in the dielectric layer, but because it is necessary to avoid excessive pull-down electrostatic force that causes direct contact between the upper and lower electrodes and cause a DC short circuit, a large electrostatic force cannot be applied, which will result in insufficient contact between the electrical contact point 2 and the signal line 7. The radio frequency performance of the switch is degraded (such as large insertion loss, too high series impedance introduced, etc.).

Contents of the invention

In order to avoid the cohesive failure caused by the charge injection and accumulation effect caused by the MEMS capacitive switch working in the Down state for a long time, at the same time, in order to make the MEMS capacitive switch work under sufficient driving voltage and ensure the RF performance of the MEMS capacitive switch, this paper The invention provides a MEMS capacitive switch with a PN junction. There is a semiconductor PN junction between the upper and lower driving electrodes of the MEMS capacitive switch, and during the electrode pull-down process, the PN junction works in a reverse bias state to form a reverse bias diode-like effect, which can avoid charge injection and enable the MEMS capacitive switch to Working under a sufficient driving voltage can ensure the close contact between the electrical contact point and the signal line, and ultimately improve the reliability and stability of the MEMS capacitive switch.

Technical scheme of the present invention is as follows:

A MEMS capacitive switch with a PN junction, comprising a cantilever beam 1 and a signal line 7 arranged on the surface of a substrate substrate 8, one end of the cantilever beam 1 is fixed on the substrate substrate 8 by an anchor point 6, and the cantilever beam 1 The other end is provided with an electrical contact point 2 capable of connecting two sections of signal lines 7; a lower drive electrode 5 is provided on the surface area of the substrate substrate 8 between the signal line 7 and the anchor point 6, correspondingly on the cantilever beam 1 The area between the anchor point 6 and the electrical contact point 2 is provided with an upper driving electrode 3, and there is a vertical semiconductor PN junction composed of a P-type semiconductor 4-1 and an N-type semiconductor 4-2 between the upper and lower driving electrodes, so The vertical semiconductor PN junction is deposited on the surface of the upper driving electrode 3 or on the surface of the lower driving electrode 5 but the area is smaller than that of the upper driving electrode 3 or the lower driving electrode 5 .

In the Up state of the MEMS capacitive switch, no DC bias driving voltage is applied between the upper and lower driving electrodes, the upper driving electrode does not generate a pull-down process, and the electrical contact point 2 is not in contact with the signal line 7; in the Down state of the MEMS capacitive switch, Due to the DC bias driving voltage applied between the upper and lower driving electrodes, the upper driving electrode 3 is pulled down under the action of electrostatic force so that the electrical contact point 2 is in close contact with the signal line 7 and the two sections of signal lines 7 are connected together. The PN junction is in a reverse bias state, that is, the P-type semiconductor 4-1 in the vertical semiconductor PN junction is in contact with the low-voltage driving electrode, while the N-type semiconductor 4-2 is in contact with the high-voltage driving electrode.

A MEMS capacitive switch with a PN junction, comprising a fixed support beam 9 and a signal line 7 arranged on the surface of a substrate substrate 8, and the two ends of the fixed support beam 9 are respectively fixed on the substrate substrate 8 through an anchor point 6 , the middle position of the fixed support beam 9 is provided with an electrical contact point 2 capable of contacting the signal line 7; the two surface areas of the substrate substrate 8 between the signal line 7 and the two anchor points 6 are respectively provided with a lower driving electrode 5. Correspondingly, an upper drive electrode 3 is provided in the two regions between the two anchor points 6 of the fixed beam 9 and the electrical contact point 2, and there is a P-type semiconductor electrode between the two pairs of upper and lower drive electrodes. A vertical semiconductor PN junction composed of 4-1 and N-type semiconductor 4-2, the vertical semiconductor PN junction is deposited on the surface of the upper driving electrode 3 or on the surface of the lower driving electrode 5 but the area is smaller than that of the upper driving electrode 3 or the lower driving electrode 5 area.

In the Up state of the MEMS capacitive switch, no DC bias driving voltage is applied between the upper and lower driving electrodes, the upper driving electrode does not generate a pull-down process, and the electrical contact point 2 is not in contact with the signal line 7; in the Down state of the MEMS capacitive switch, Since a DC bias driving voltage is applied between the upper and lower driving electrodes, the two upper driving electrodes 3 are pulled down under the action of electrostatic force so that the electrical contact point 2 is in close contact with the signal line 7, and at the same time, the vertical semiconductor PN junction is in a reverse bias state. That is, in the vertical semiconductor PN junction, the P-type semiconductor 4-1 is in contact with the low-voltage driving electrode, while the N-type semiconductor 4-2 is in contact with the high-voltage driving electrode.

Working principle of the present invention is (taking the MEMS capacitive switch with cantilever beam as example):

When the MEMS capacitive switch with PN junction provided by the present invention is in the Up state (switch off state), no DC bias driving voltage is applied between the upper and lower driving electrodes, and a certain distance is kept between the upper driving electrode and the lower driving electrode. There is no contact between the contact point 2 and the signal line 7. At this time, the radio frequency signal on one section of the signal line cannot be transmitted to another section of the signal line. When a DC bias driving voltage is applied between the upper and lower driving electrodes, an electrostatic attraction is generated due to the electric field between the upper and lower driving electrodes, so that the upper driving electrode is pulled down under the action of electrostatic attraction, and the MEMS capacitive switch is in Down state at this time. In the closed state (switch closed state), the electrical contact point 2 is in close contact with the signal line 7 and connects the two sections of signal lines, eventually causing the radio frequency signal on one section of the signal line to be transmitted to the other section of the signal line.

The DC bias driving voltage applied between the upper and lower driving electrodes should satisfy:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; 27</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; A</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}$

Where k is the elastic coefficient of the structure composed of the driving plate and the supporting beam, _ε0 is the vacuum permittivity, A is the area of the upper and lower plates, and h is the initial distance between the two electrodes.

The electrostatic attraction (electric field force) on the upper driving electrode is:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; AV</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

where g is the gap between the plates. For the switch electrode structure in the present invention, the gap heights of the PN junction part and the non-PN junction part are inconsistent, so it is better to calculate the electrostatic force separately. The gap height of the PN junction part is the thickness of the P-type semiconductor plus the thickness of the air gap, as shown in g' in Figure 3 and Figure 4.

When the MEMS capacitive switch with PN junction provided by the present invention is in the Down state (switch closed state), it should ensure that the vertical PN junction is in contact with the upper and lower drive electrodes, and the vertical PN junction is in the reverse bias state, that is, the P-type in the vertical semiconductor PN junction. The semiconductor 4-1 is in contact with the low-voltage driving electrode, while the N-type semiconductor 4-2 is in contact with the high-voltage driving electrode. At this time, the vertical semiconductor PN junction is similar to a reverse-biased diode, and there will be no charge injection and accumulation effects, so The problem of bonding failure of the upper and lower driving electrodes existing in the existing MEMS capacitive switch is avoided. In the Down state, the upper and lower plates are in close contact with the PN junction. Due to the reverse bias of the longitudinal PN junction, there is still a DC voltage difference between the upper and lower electrodes. At the same time, because the area of the longitudinal PN junction is smaller than the area of the driving electrode, the area of the vertical PN junction is removed by the upper and lower driving electrodes. There is still electrostatic attraction between the remaining areas, and this electrostatic attraction only needs to keep the switch closed (Down state), that is, this electrostatic attraction must be greater than the restoring force F _r of the cantilever beam 1 . Among them, the simple model of restoring force F _r is:

F _r =k _e (g ₀ -g)

Among them, k _e is the equivalent elastic coefficient after taking into account the stretching, and g ₀ is the electrode gap in the UP state. Although the mechanical restoring force generated by the adsorption force and repulsion force between the metal and the dielectric layer is not fully understood for the switch in close contact, it can still be assumed in the calculation that t _d is the thickness of the PN junction, and g = t _d .

At this time, in the pull-down state, the remaining area on the electrode except the PN junction area is A'. At this time, the electrostatic force formula is

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

The calculation of the rest of the parameters of the switch is the same as the calculation process of the switch design under normal circumstances.

In summary, the beneficial effects of the present invention are:

The MEMS capacitive switch with PN junction provided by the present invention, since there is a PN junction with an area smaller than that of the driving electrodes between the upper and lower driving electrodes, when a DC bias driving voltage is applied between the upper and lower driving electrodes, the upper and lower driving electrodes can obtain Sufficient electrostatic force will pull down the upper driving electrode, so as to ensure the close contact between the electrical contact point and the signal line; at the same time, in the Down state of the MEMS capacitive switch, the vertical PN junction between the upper and lower driving electrodes is in a reverse bias state, making it generate Similar to the characteristics of a reverse-biased diode, there will be no charge injection and accumulation, thereby avoiding the problem of bonding failure of the upper and lower drive electrodes. Therefore, the MEMS capacitive switch with PN junction provided by the present invention can improve its reliability and stability compared with the existing MEMS capacitive switch.

Description of drawings

FIG. 1 is a schematic structural diagram of a MEMS capacitive switch with a conventional contact-driven pull-down electrode structure.

FIG. 2 is a structural schematic diagram of a MEMS capacitive switch with a conventional non-contact driving pull-down electrode structure.

FIG. 3 is a schematic diagram of a MEMS capacitive switch (cantilever beam structure) with a PN junction provided by the present invention (the PN junction is deposited on the surface of the upper driving electrode).

FIG. 4 is a schematic diagram of a MEMS capacitive switch (cantilever beam structure) with a PN junction provided by the present invention (the PN junction is deposited on the surface of the lower driving electrode).

FIG. 5 is a top view of a MEMS capacitive switch (cantilever beam structure) with a PN junction provided by the present invention.

FIG. 6 is a schematic diagram of the structure of the electrodes when the MEMS capacitive switch (cantilever beam structure) with a PN junction is closed (Down state) provided by the present invention.

FIG. 7 is a schematic diagram of a MEMS capacitive switch (fixed beam structure) provided by the present invention with a PN junction.

In Figure 1 to Figure 7, 1 represents the cantilever beam, 2 represents the electrical contact point, 3 represents the upper driving electrode, 4 represents the insulating dielectric layer, and 4' represents the non-contact driving MEMS capacitive switch with pull-down electrode structure driving up and down in the Down state The gap between the electrodes, 4-1 represents the P-type semiconductor, 4-2 represents the N-type semiconductor, 5 represents the lower driving electrode, 6 represents the anchor point, 7 represents the signal line, 8 represents the substrate substrate, and 9 represents the fixed support beam .

detailed description

Below in conjunction with accompanying drawing, the present invention will be further described. As shown in Figure 3 to Figure 5,

A MEMS capacitive switch with a PN junction, comprising a cantilever beam 1 and a signal line 7 arranged on the surface of a substrate substrate 8, one end of the cantilever beam 1 is fixed on the substrate substrate 8 by an anchor point 6, and the cantilever beam 1 The other end is provided with an electrical contact point 2 capable of connecting two sections of signal lines 7; a lower drive electrode 5 is provided on the surface area of the substrate substrate 8 between the signal line 7 and the anchor point 6, correspondingly on the cantilever beam 1 The area between the anchor point 6 and the electrical contact point 2 is provided with an upper driving electrode 3, and there is a vertical semiconductor PN junction composed of a P-type semiconductor 4-1 and an N-type semiconductor 4-2 between the upper and lower driving electrodes, so The vertical semiconductor PN junction is deposited on the surface of the upper driving electrode 3 or on the surface of the lower driving electrode 5 but the area is smaller than that of the upper driving electrode 3 or the lower driving electrode 5 .

In the Up state of the MEMS capacitive switch, no DC bias driving voltage is applied between the upper and lower driving electrodes, the upper driving electrode does not generate a pull-down process, and the electrical contact point 2 is not in contact with the signal line 7; in the Down state of the MEMS capacitive switch, Due to the DC bias driving voltage applied between the upper and lower driving electrodes, the upper driving electrode 3 is pulled down under the action of electrostatic force so that the electrical contact point 2 is in close contact with the signal line 7 and the two sections of signal lines 7 are connected together. The PN junction is in a reverse bias state, that is, the P-type semiconductor 4-1 in the vertical semiconductor PN junction is in contact with the low-voltage driving electrode, while the N-type semiconductor 4-2 is in contact with the high-voltage driving electrode.

Fig. 3 shows the MEMS capacitive switch (cantilever beam structure) schematic diagram with PN junction that the present invention provides, and wherein PN junction is deposited on the upper drive electrode surface; The area of the upper drive electrode 3.

Fig. 4 shows the MEMS capacitive switch (cantilever beam structure) schematic diagram with PN junction that the present invention provides, and wherein PN junction is deposited on the lower drive electrode surface; The area of the lower drive electrode 5.

FIG. 5 is a top view of a MEMS capacitor with a PN junction (cantilever beam structure) provided by the present invention.

FIG. 6 is a schematic diagram of a partial electrode structure of the MEMS capacitive switch with a PN junction when it is pulled down (DOWN state) provided by the present invention. Between the upper and lower plates 3 and 5 of the electrode is a PN junction working in a reverse bias state, and the suspended part between the upper and lower driving electrodes generates a continuous pulling force to keep the switch closed and the signal continuously turned on.

FIG. 7 is a schematic diagram of a MEMS capacitor with a PN junction (fixed beam structure) provided by the present invention.

A MEMS capacitive switch with a PN junction, comprising a fixed support beam 9 and a signal line 7 arranged on the surface of a substrate substrate 8, and the two ends of the fixed support beam 9 are respectively fixed on the substrate substrate 8 through an anchor point 6 , the middle position of the fixed support beam 9 is provided with an electrical contact point 2 capable of contacting the signal line 7; the two surface areas of the substrate substrate 8 between the signal line 7 and the two anchor points 6 are respectively provided with a lower driving electrode 5. Correspondingly, an upper drive electrode 3 is provided in the two regions between the two anchor points 6 of the fixed beam 9 and the electrical contact point 2, and there is a P-type semiconductor electrode between the two pairs of upper and lower drive electrodes. A vertical semiconductor PN junction composed of 4-1 and N-type semiconductor 4-2, the vertical semiconductor PN junction is deposited on the surface of the upper driving electrode 3 or on the surface of the lower driving electrode 5 but the area is smaller than that of the upper driving electrode 3 or the lower driving electrode 5 area.

In the Up state of the MEMS capacitive switch, no DC bias driving voltage is applied between the upper and lower driving electrodes, the upper driving electrode does not generate a pull-down process, and the electrical contact point 2 is not in contact with the signal line 7; in the Down state of the MEMS capacitive switch, Since a DC bias driving voltage is applied between the upper and lower driving electrodes, the two upper driving electrodes 3 are pulled down under the action of electrostatic force so that the electrical contact point 2 is in close contact with the signal line 7, and at the same time, the vertical semiconductor PN junction is in a reverse bias state. That is, in the vertical semiconductor PN junction, the P-type semiconductor 4-1 is in contact with the low-voltage driving electrode, while the N-type semiconductor 4-2 is in contact with the high-voltage driving electrode.

Claims (2)

1. a kind of mems capacitance switch with pn-junction, including cantilever beam (1) be arranged at two sections of substrate base (8) surface letters Number line (7), one end of cantilever beam (1) is fixed on substrate base (8) by anchor point (6), and the other end of cantilever beam (1) is provided with The electrical pickoff (2) that two segment signal lines (7) can be coupled together；Substrate base between holding wire (7) and anchor point (6) (8) surface region is provided with lower drive electrode (5), between the corresponding anchor point (6) in cantilever beam (1) and electrical pickoff (2) Region is provided with drive electrode (3), has one by p-type semiconductor (4-1) and n-type semiconductor between upper and lower drive electrode (4-2) the longitudinal semiconductor pn junction constituting；

Under the off-state of mems capacitance switch, do not apply direct current biasing driving voltage, upper drive between upper and lower drive electrode Moving electrode does not produce downdraw process, and electrical pickoff (2) is not contacted with two segment signal lines (7)；Closure in mems capacitance switch Under state, due to being applied with direct current biasing driving voltage between upper and lower drive electrode, upper drive electrode (3) is under electrostatic force It is pulled down into so that electrical pickoff (2) is in close contact with holding wire (7) and couples together two segment signal lines (7), longitudinally partly simultaneously Conductor pn-junction is in reverse-biased, i.e. p-type semiconductor (4-1) and low voltage drive contact electrode in longitudinal semiconductor pn junction, And n-type semiconductor (4-2) and high voltage drive contact electrode；

Described longitudinal semiconductor pn junction is deposited on drive electrode (3) surface or is deposited on lower drive electrode (5) surface but area Area less than upper drive electrode (3) or lower drive electrode (5).

2. a kind of mems capacitance switch with pn-junction, including clamped beam (9) with the holding wire that is arranged at substrate base (8) surface (7), the two ends of clamped beam (9) are fixed on substrate base (8) by an anchor point (6) respectively, and clamped beam (9) interposition installs It is equipped with the electrical pickoff (2) that can contact with holding wire (7)；Substrate base between holding wire (7) and two anchor points (6) (8) two surface regions are respectively arranged with a lower drive electrode (5), corresponding two anchor points (6) in clamped beam (9) and electricity Two regions between contact point (2) are respectively arranged with a upper drive electrode (3), two to upper and lower drive electrode between respectively There is a longitudinal semiconductor pn junction being made up of p-type semiconductor (4 1) and n-type semiconductor (4 2)；

Under the off-state of mems capacitance switch, do not apply direct current biasing driving voltage, upper drive between upper and lower drive electrode Moving electrode does not produce downdraw process, and electrical pickoff (2) is not contacted with holding wire (7)；Closure state in mems capacitance switch Under, due to being applied with direct current biasing driving voltage between upper and lower drive electrode, two upper drive electrodes (3) are under electrostatic force It is pulled down into so that electrical pickoff (2) is in close contact with holding wire (7), longitudinal semiconductor pn junction is in reverse-biased simultaneously, that is, indulge P-type semiconductor (4-1) and low voltage drive contact electrode in semiconductor pn junction, and n-type semiconductor (4-2) is driven with high voltage Moving electrode contacts；

Described longitudinal semiconductor pn junction is deposited on drive electrode (3) surface or is deposited on lower drive electrode (5) surface but area Area less than upper drive electrode (3) or lower drive electrode (5).