RU2721303C1 - Optically-controlled switch of millimeter range with built-in light source, based on transmission line with semiconductor substrate - Google Patents

Abstract

FIELD: radio equipment.SUBSTANCE: optically-controlled switch comprises bottom-up: substrate made of semiconductor material, which in the absence of an external action acts as a dielectric, a first conductive layer of the transmission line made of a conductive material on the upper side of the substrate, and a laser. Laser comprises an upward bottom: a lower distributed Bragg reflector (DBR) of the laser, which is partially translucent to enable laser light emitting through the lower DBR, an active laser region, and a completely reflecting upper DBR laser. In the substrate, in the beam falling zone, there is a photoconductive portion which, when illuminated with light, is in a conductor state, and in the absence of light is in a dielectric state, in the first conductive layer of the transmission line in the beam incidence region, at least one radiation window is made to allow the laser light to pass to the photoconductive region.EFFECT: technical result consists in enabling reduction of introduced losses, reduction of power consumption, improvement of isolation between ON / OFF states, increase in switching speed, increase of operating frequency band, reduction of dimensions.20 cl, 16 dwg

Description

FIELD OF THE INVENTION

The present invention relates to radio engineering, and more specifically to an optically controlled millimeter-wave switch based on a transmission line with a semiconductor substrate.

State of the art

Currently, active development of millimeter-band networks and devices, such as 5G and 6G, WiGig, radars for autonomous navigation, etc., is underway. The appearance of such new applications in the millimeter range for frequencies above 30 GHz (EHF, or EHF) requires the development of a new class of elements and circuits (active elements, antennas, printed circuit boards, feeders and switching devices) that can integrate data transmission, detection capabilities and search capabilities optimal transmission direction within a single device. In particular, for many applications, the switch is an important component because it allows you to control the switching of the distribution channels of the signal.

Meanwhile, at frequencies above 30 GHz, the technological features of the device design are of great importance, since the propagating wavelengths are very small, and any inhomogeneities in the paths that would not be significant for lower frequencies can lead to spurious and noise effects, to avoid which it is required production of high-precision transmission lines with low losses per unit length. Accordingly, prior art switches for lower frequencies become unsuitable due to high losses.

Known solutions without optical control for frequencies above 30 GHz are extremely complex and expensive, therefore, among the available technologies for the millimeter range, optically controlled switches on SIW structures are of particular interest (see, for example, US 2019/086763 A1, 09/12/2018, Samsung Electronics), since in the range for which they are intended (from about 10 to 40 GHz) they have a simple design and manufacture; economical way to embed in a single dielectric substrate; lack of complex transitions; wide band of frequencies; ease of integration with classic printed circuit board (PCB) technologies, as well as good isolation of power / control circuits from the RF path, low losses, high permissible transmit power. Such a switch comprises a printed circuit board including an upper and lower layer and a dielectric layer between the upper and lower layers, a plurality of transition metallized holes electrically connected to the upper and lower layers and arranged in at least two rows, a shorting metallized hole electrically connected to the lower a layer and separated from the upper layer by a dielectric gap, and a photoconductive element electrically connected to the upper layer and a shorting hole, the photoconductive element having a dielectric state and a conductor state, and wherein the electromagnetic wave supplied to the optically controlled switch propagates through a waveguide formed between said at least two rows, or blocked in it. However, at frequencies above 30–40 GHz, spurious radiation occurs in such a switch both through a partially closed and a completely closed dielectric gap, because the photoconductive element covering it is made of materials having a relatively high dielectric constant (for example, about 12 for silicon), which creates radiation conditions for a given gap as for a ring emitter. Because of this, losses increase, matching in the RF path in the open state worsens, sensitivity to external pickups increases, isolation between the ON / OFF states worsens, and a large optical power from the control light source is required, which leads to its heating and a decrease in the working life.

The above disadvantages are largely due to the fact that this switch, like most existing radio frequency devices existing in the prior art, is based on printed circuit board (PCB) manufacturing technologies, while the latter have certain limitations for frequencies above 30 GHz. Known problems of such technologies are as follows.

- Uncontrolled etching of copper lines does not allow for high manufacturing accuracy, limited at best to ~ +/– 20 μm, which leads to insufficient accuracy of the width of copper strips and positioning of VIA (transition metallized holes), non-observance of the required width of the gaps in metallization, as well as significant surface roughness. This is critical for frequencies above 30 GHz, since at these frequencies all these manufacturing inaccuracies are inhomogeneities, due to which the real characteristics of the transmission line deviate from the calculated ones and high losses appear in the dielectric and in the conductors.

- The thickness of copper lines in traditional PCB technologies is relatively large, due to which parasitic reactance arises at frequencies above 30 GHz, which has to be compensated using additional components, which in turn leads to additional losses, larger dimensions and narrowing bandwidth.

- For effective line switching, a large amount of photoconductive material is required, as a result of which there is a limit to the speed of the switch.

- Recently, a surface-emitting laser with a vertical resonator (or simply a vertically-emitting laser, VCSEL) has gained popularity. It is very convenient for practical use to use the grating of such VCSEL lasers, however, the low packing density of the supply lines and switches on the printed circuit board leads to the fact that only a small amount of VSCEL is used from the entire grating, which leads to an increase in the size of the required VCSEL grating, and, accordingly, to increase its value.

- The dielectric substrates available on the market for printed circuit boards have a relatively large thickness, which complicates the miniaturization of EHF devices and EHF lines.

Accordingly, the existing EHF switches on the market are cumbersome, complex and expensive, have very high losses, and are also inconvenient for integration due to the need to decouple power / control circuits.

From the prior art, at present, there were no known EHF switches available on the market in the range> 70 GHz, capable of performing the function of a public – private key for waves passing through it in a pure form and which would not be subject to the above problems. Only similar solutions are known from the related field, which can be considered as partially solving these problems.

So, for example, in US patent 9,431,564 B2 (08/30/2016, Thales Holding UK PLC) a photoconductive switch is disclosed comprising a photoconductive material and first and second contacts provided on said photoconductive material, wherein said first and second contacts contain a plurality of intersecting tracks, moreover, the tracks of each contact are separated from the tracks of the other contact by a photoconductive gap, the paths are bent so that the minimum photoconductive gap measured in any direction remains almost the same regardless of t orientation directions. However, the function of this switch is only modulation of millimeter waves passing through it, and it is not suitable for their complete blocking, since it has a stray capacitance, due to which additional leakage of waves arises and insulation is degraded.

US Pat. No. 9,716,202 B2 (July 25, 2017, The Curators of the University of Missouri, Columbia, MO) discloses a solid-state optically controlled switch that can be used as a power limiting switch in various applications or as a high power switch. In particular, this switch utilizes the photoconductive properties of the semiconductor to provide a linear limiting function. In one embodiment, the switch configuration provides for an off-state transmission of more than 99.9999% of the transmitted signal and an on-state restriction of up to less than 0.0001% of the transmitted signal. This switch is closest to the present invention. The difference in essence and implementation of this well-known solution is that its application is reduced only to a power limiter, in which the signal should not be reflected, but either absorbed or diverted to attenuators, and for it to work efficiently, the semiconductor material in it should contain nitride that requires large optical power to activate the switch. In addition, this document does not describe how to make a switch with an integrated light source, and the allegedly coplanar structure described is not really such, since it does not imply a configuration of the coplanar transmission line for distributing the electromagnetic field in its cross section at high frequencies, but It’s just a conductor, partially surrounded by ground to divert part of the signal.

SUMMARY OF THE INVENTION

In order to eliminate at least some of the aforementioned drawbacks of the prior art, the present invention is directed to the creation of an optically controlled EHF switch made by a more accurate technology based on a transmission line with a semiconductor substrate and having an integrated light source.

According to a first aspect of the present invention, there is provided an optically controlled switch comprising from bottom to top: a substrate made of a semiconductor material which, in the absence of external influences, acts as a dielectric, a first conductive layer of a transmission line made of a conductive material on the upper side of the substrate, and a laser, comprising from bottom to top: a lower distributed Bragg reflector (DBR) of the laser, partially translucent to allow light emission zera through the lower DBR, the active region of the laser, and the upper DBR of the laser, made completely reflective, and in the substrate in the zone of incidence of the beam a photoconductive section is made, which when illuminated with light is in the state of the conductor, and in the absence of light is in the state of the dielectric, in the first conducting at least one radiation window is made in the layer of the transmission line in the zone of incidence of the beam to ensure the passage of laser light to the photoconductive section.

In one embodiment, the substrate is made of highly resistive photoconductive material.

In one embodiment, the transmission line is a coplanar waveguide (CPW), the first conductive layer comprising a coplanar line containing a central signal conductor extending above the photoconductive section and semi-infinite earth conductors surrounding it, said substrate being the dielectric layer for CPW.

In one embodiment, the switch further comprises: a connecting layer made of a translucent dielectric between the first conductive layer and the lower DBR.

In one embodiment, the connection layer is made of a dielectric film.

In one embodiment, the transmission line is a coplanar waveguide (CPW), the first conductive layer comprising a coplanar line containing a central signal conductor extending above the photoconductive section and semi-infinite earth conductors surrounding it, the connecting layer being the dielectric layer for CPW.

In one embodiment, the switch further comprises: a second conductive layer made of a conductive material between the connecting layer and the lower DBR, wherein at least one radiation window is formed in the second conductive layer of the transmission line in the incident region of the beam to allow the laser light to pass to the photoconductive area, the first conductive layer is the signal layer of the transmission line, and the second conductive layer is the ground layer of the transmission line.

In one embodiment, the transmission line is a co-planar waveguide with an earth layer (GCPW), the signal layer comprising a coplanar line containing a central signal conductor extending above the photoconductive section and semi-infinite earth conductors surrounding it.

In one embodiment, the transmission line is a microstrip line, wherein the signal layer comprises two segments of the microstrip line separated by a photoconductive section.

In one embodiment, the switch further comprises: a second conductive layer made of conductive material on the lower side of the substrate, the transmission line being a waveguide with pin walls (SIW), the first conductive layer being the top wall of the SIW and the second conductive layer being the bottom wall SIW, moreover, the dielectric layer for SIW is said substrate.

In one embodiment, the switch further comprises: side walls formed by rows of transition metallized holes (VIA) made in the substrate between the first and second conductive layers on opposite sides of the photoconductive section.

In one embodiment, the switch further comprises: at least one additional laser and at least one corresponding additional photoconductive portion located adjacent to said laser and said photoconductive portion between the side walls of the SIW to form a reflective wall.

In one embodiment, the switch further comprises: a connecting film formed between the active region of the laser and the lower DBR.

In one embodiment, the thickness of the substrate is equal to the depth of light absorption at the working wavelength of the laser, taking into account the diffusion length of the charge carriers in the photoconductive region.

In one embodiment, the width of the conductors in the first conductive layer, the size of the laser aperture, and the diffusion length of the charge carriers in the photoconductive section are of the same order.

In one of the embodiments, the photoconductive section is made in the substrate using the method of introducing new recombination centers into the semiconductor.

In one embodiment, the substrate as a whole has a carrier lifetime of free carriers in the semiconductor that exceeds the carrier lifetime required to form a photoconductive region with predetermined characteristics, and the photoconductive region is made in the substrate using the method of introducing new recombination centers into the semiconductor in the beam incidence zone.

In one embodiment, the substrate as a whole has a lifetime of free carriers in the semiconductor equal to or less than the carrier lifetime required to form a photoconductive region with predetermined characteristics, and the photoconductive region is made in the substrate using the method of introducing new recombination centers along the boundary around the semiconductor areas of incidence of the beam.

According to a second aspect of the present invention, there is provided a high-frequency switching device comprising a plurality of optically controlled switches according to claim 1, made on the basis of a single substrate and containing interconnected transmission lines.

According to a third aspect of the present invention, there is provided a reconfigurable optically controllable switch comprising a lattice of optically controllable switches according to the first aspect, made on the basis of a single substrate, in which at least a portion of the adjacent optically controllable switches are configured to, when turned on, form SIW side walls.

Technical result

The present invention provides an inexpensive optically-controlled switch that is capable of operating in the mm range at frequencies above 30 GHz, while demonstrating improved characteristics such as reduced insertion loss, reduced power consumption, improved isolation between ON / OFF states, increased switching speed, increased working frequency band, reduction in size, easy integration into SoI and CMOS devices.

Brief Description of the Drawings

The present invention will now be described in more detail with reference to the accompanying drawings, in which:

In FIG. 1A – 1B show an optically controlled switch according to the present invention.

In FIG. 2A – 2B show embodiments of a transmission line in a serial type and parallel type switch.

In FIG. 3A – 3B show the principle of operation of the series-type switch of FIG. 2A.

In FIG. 4A – 4B illustrate the operation principle of the sequential type switch of FIG. 2B.

In FIG. Figure 5 shows an example of the distribution of excited carriers in the bulk of a silicon material.

In FIG. Figure 6 shows the results of modeling the concentration of carriers in the bulk of the photoconductive material.

In FIG. 7 shows an exemplary conduction distribution in the illuminated region in a switch based on the GCPW line.

In FIG. 8 presents the simulation results of the S – parameters of the switch of FIG. 7.

In FIG. 9A – 9C show embodiments of conductive layers in the proposed switch.

In FIG. 10A – 10C show embodiments of a signal conductor in a coplanar line.

In FIG. 11A – 11D show an embodiment of a switch based on an SIW line.

In FIG. 12 shows an embodiment of a reflective wall in a switch based on an SIW line.

In FIG. 13A – 13B show a reconfigurable SIW-based switch without VIA.

In FIG. 14 shows an example of a phase shifter using sequential type switches.

In FIG. 15–16 show examples of local processing of a silicon substrate.

It should be understood that the figures can be presented schematically and not to scale and are intended mainly to improve understanding of the present invention.

Detailed description

The structure of the optically controlled switch according to the present invention is shown in FIG. 1A – 1B. So, the switch is a multilayer device containing enlarged three layers (Fig. 1B): the lower layer 1 in the form of a semiconductor substrate (wafer), the middle layer 2 in the form of a connecting (fastening) structure, in which half of the laser structure with a translucent mirror is also made (reflector), and the upper layer 3 in the form of a second laser part with a fully reflective mirror. As shown in FIG. 1A, the lower layer 1 (substrate) is made of a highly resistive semiconductor material, such as silicon, which under normal conditions, in the absence of external influence, should act as a dielectric. The middle layer 2 (connecting structure) contains a signal layer 4 made on the aforementioned substrate 1, a dielectric connecting layer 5, for example a silicon oxide film, an earth layer 6, a lower (partially translucent) distributed Bragg reflector (DBR) 7 and a connecting film (connecting interface) , bonding interface) 8. At the same time, gold, silver, copper and any other conductors that can be applied to these substrates with a given accuracy can be used to manufacture the conductors of the signal and ground layers. The upper layer 3 (light source) contains the active region 9 and the upper (fully reflective) DBR 10.

As you can see, this structure resembles a VCSEL laser with lower radiation, with the difference that a transmission line is built into the middle layer. Accordingly, the basic principle of the present invention is that on the same semiconductor substrate as the RF (radio frequency) line, it is possible to grow part of the VCSEL structures (single, or a set, or an entire lattice).

On the substrate 1 of highly resistive silicon, for example, using the method of electronic lithography, the conductors of the signal RF line 4 are deposited. Next, a layer of silicon oxide 5 of a fixed thickness is grown on this structure. The thickness of the silicon oxide and the width of the conductors of the RF line are selected to comply with the required line impedance (for example, 50 Ohms). On the silicon oxide layer 5, the metallization of the earth layer 6 is applied with the necessary window for the passage of the light beam from the laser. Next, a partially translucent distributed Bragg reflector (DBR) structure is grown on this structure. 7. A connecting film 8 is grown on its surface. Independently of this structure, the second part of the laser is manufactured: laser active medium 9 and an opaque distributed reflector 10. This structure can be grown, for example, on a GaAs substrate or other optically opaque substrate. Then, these two parts of the laser are connected through a connecting film 8 or otherwise.

The upper DBR 10 has a very high reflection coefficient (for example, more than 99.9%) for full light reflection, and the lower DBR 7 has a lower reflection coefficient (for example, about 95%) to allow laser light to be emitted through the lower DBR. Also, to ensure the passage of laser light in the signal layer 4 and in the ground layer 6, holes or gaps (radiation windows) 12 are made, and the connecting structure 5 is translucent. At the same time, the connecting structure 5 should act as a dielectric layer between the signal layer 4 and the ground layer 6 of the microstrip transmission line. Accordingly, for such purposes, the connecting structure 5 should be made of a translucent dielectric, such as silicon oxide, SiO ₂ . Thus, the light from the laser can pass to the substrate 1.

A photoconductive section 11 having a photoconductivity effect is made in the substrate in the zone of incidence of the beam. This means a change in the state of the photoconductive region when illuminated with light: without light, it is in a dielectric state, in light it is in a conductor state. Due to this, it is possible to create switched structures (reflecting or transmitting) for the radio frequency signal.

From the point of view of the transmission line, the switch can be of a sequential type (when 2 separate segments of the transmission line are connected by a switching element) or of a parallel type (when a transmission line is shunted by a switching element). Further in FIG. 2A – 2B show embodiments of a transmission line in a switch, respectively, of a serial type and a parallel type. In both types, the ground layer, which is solid, has an opening 13 for transmitting light from the laser to the photoconductive section 11 (not shown in FIG. 2B for simplicity). As for the signal layer 4, for example, a conventional microstrip line is used in the serial type switch (Figs. 1A – 1B, 2A), in which a gap 12 is made in the region of the photoconductive section 11 (or, in other words, two segments of the microstrip line are separated photoconductive section 11). A parallel type switch uses, for example, a coplanar ground layer waveguide (GCPW), in which the signal layer 4 comprises a coplanar line containing a central signal conductor passing over the photoconductive section and the semi-infinite earth conductors surrounding it (Fig. 2B).

The principle of operation of the series-type switch of FIG. 2A is shown in FIG. 3A – 3B. In particular, in state 1 (OFF), when no power is supplied to the VCSEL, the VCSEL does not emit - accordingly, the light does not fall on the photoconductive section 11, and the photoconductive section 11 is in the dielectric state. The microstrip line 4 is open, and the signal 14 arriving at the input of the switch is reflected from such a dielectric gap 12 without reaching the output.

In contrast, in state 2 (ON), when power is supplied to the VCSEL, the VCSEL emits light 15, which through the hole 13 in the ground layer 6, the connecting layer 5 and the gap 12 in the signal layer 4 falls on the photoconductive section 11. Photoconductive section 11 goes into the state of the conductor, thereby closing the gap 12 in the microstrip line, and the signal 14 received at the input of the switch is output.

The principle of operation of the parallel type switch of FIG. 2B is shown in FIG. 4A – 4B. For ease of understanding, the light source is not shown here. In state 1 (OFF), when no power is supplied to the VCSEL, the VCSEL does not emit - accordingly, the light does not fall on the photoconductive section 11, and the photoconductive section 11 is in the dielectric state. The gap 12 between the signal conductor of the coplanar line and the earth conductors remains non-conductive, and the signal received at the input of the switch is output.

In state 2 (ON), when power is supplied to the VCSEL, the VCSEL emits light 15, which through the hole 13 in the ground layer 6, the connecting layer 5 and the gap 12 between the signal conductor of the coplanar line and the ground conductors falls on the photoconductive section 11. Photoconductive section 11 goes into the state of the conductor, thereby closing the gap 12, and the signal received at the input of the switch is shorted to ground.

The miniaturization of such a switch, created by placing a small transmission line and a light source on a semiconductor substrate, is achieved when, in order to maintain a balance between the optical power of the light source, the size of its aperture, and the attainable conduction band area in the photoconductor, the following three values have the same same order:

1) the width of the signal conductors (in an exemplary embodiment, the transmission line width in the signal layer is of the order of 10 μm);

2) the aperture size of the light source (in an exemplary embodiment, the VCSEL beam diameter is about 10 μm);

3) the diffusion length in the semiconductor material (it is determined by the carrier lifetime and the recombination rate, as will be explained in more detail below) (in an exemplary embodiment, the dimensions of the photoconductive section are 10x10x10 microns).

The problem of choosing specific values of these three values can be solved by determining the sizes of the photoconductive section and the width of the signal conductors for given known characteristics of the selected light source (its aperture size, radiation power, wavelength), taking into account the selected materials and manufacturing technology, so that the laser power is sufficient to close / open the line, and also to provide the required characteristics of the switch.

To simplify the calculations, choosing a cube of size d as the active zone of the photoconductive region where it is necessary to provide the specified characteristics (that is, in which edge effects do not work), we can estimate its parameters when excited by light.

The electrical resistance R and the electric capacitance C between the parallel faces of such a cubic section can be estimated by the following relations:

, (1)

, (1)

, (2)

, (2)

where σ is the conductivity,

ε is the relative dielectric constant

ε ₀ - dielectric constant in free space.

In this case, the conductivity σ of the photoconductive section is calculated by the following formula:

, (3)

, (3)

where n is the concentration of carriers

e is the elementary electric charge (fixed value),

μ is the carrier mobility (a fixed value for a given semiconductor).

In turn, the Helmholtz equation can be used to determine the concentration of n carriers:

, (4)

, (4)

where Φ is the lighting function.

The boundaries of the photoconductive section, in fact, are determined by the diffusion length s :

, (5)

, (5)

where D is the diffusion coefficient,

τ is the lifetime of charge carriers in the photoconductive material.

The estimate for the required power consumption is:

(6)

(6)

The ratio of the sizes of the light source and the photoconductive section affects the required optical power. With the same size of the light source and with different sizes of the photoconductive section, different optical power is needed to provide a given concentration of carriers.

In addition to diffusion, the size of the photoconductive region can be limited by modulating the carrier lifetime in a semiconductor. The lifetime in the semiconductor volume can be reduced, for example, by introducing defects into its crystal structure. Moving / pushing the boundaries of the photoconductive (region with a small volumetric lifetime) section from the zone in which it is necessary to provide a given level of conductivity, using recombination edge effects, one can increase / decrease the effective carrier lifetime and increase / decrease the total switch on / off time.

Therefore, depending on the purpose of the destination device, by selecting the geometrical parameters of the photoconductive section, the transmission line and the light source, it is possible to optimize the consumed optical power of the switch and its on / off time.

Above, the disadvantages of the prior art indicated the need to switch from the traditional dimensions of the transmission line to micron sizes in order to switch to higher operating frequencies, to increase manufacturing accuracy, to reduce spurious reactances associated with the thickness of the conductors. The transition to the technologies used for the production of semiconductor devices can solve the problems of limited accuracy in the manufacture of printed circuit boards, as well as provide micron sizes for the switch and transmission lines of the device.

Given the above requirements and technology, in a specific example, a laser available on the market with an aperture of 10 μm, a power of 10 mW, and a wavelength of 850 nm is selected as the light source. Accordingly, as the zone of the photoconductive section where it is required to provide the specified characteristics, we choose a cube with a side d = 10 μm, which is 100 times smaller than the dimensions of the photoconductive elements known from the prior art.

d ₀ = 1000 μm → 10 ^–2 d ₀ = 10 μm.

The volume of the excitation region, respectively:

V ₀ → 10 ^–6 V ₀ .

Given the above relations (1) and (2), the parasitic resistance of the calculated area increases by 100 times compared with the resistance R _{0 of the} traditional photoconductive element, and the parasitic capacitance decreases by 100 times.

R ₀ → 100 R ₀ .

C ₀ → 0.01 C ₀ .

As you can see, such scaling positively affects the parasitic capacitance, reducing it, but negatively affects the resistance. To reduce the resistance, returning its value to acceptable, without changing the size of the site, it is necessary to increase its conductivity, as follows from (1).

σ ₀ → 100 σ ₀ .

Such conductivity, based on relations (3) and (4), is provided with a corresponding increase in carrier concentration:

n ₀ → 100 n ₀ .

Then, in the considered volume of 10 ^–6 V _{0, the} number of carriers transferred to the excited state should be:

N ₀ → 10 ^–4 N ₀ .

For a given (constant) power of the light source P ₀ , in accordance with relation (6), it is necessary that the carrier lifetime in this material be

τ ₀ → 10 ^–4 τ _0.

The requirement to reduce the lifetime of minority carriers supports the miniaturization of the switch, since it determines the diffusion length of the carriers in the material, i.e. actual size of the conduction band in the material. This can be used when choosing the size of the aperture of the light source, which can be smaller than the size of the necessary active zone switching to the length of the diffusion propagation of carriers in the photoconductor.

The lifetime of minority carriers also determines the duration of the processes of excitation and recombination of carriers in the material. Therefore, the requirement to reduce 10 ^–4 τ ₀ makes it possible to increase by ~ 10,000 times the switching speed of the photoconductive section (and, accordingly, the switch), at the same light source power.

As an example of calculation, when silicon is chosen as the photoconductive material, with a diffusion coefficient for small regions of 29 cm ² / s and a carrier lifetime of 1 μs, the diffusion length will be approximately 54 μm, which is comparable with the required size of the photoconductive section.

In FIG. 5 illustrates an example of the distribution of excited carriers in the bulk of the same silicon material for the case when the above-mentioned commercially available laser with an aperture of 10 μm, 10 mW, and a wavelength of 850 nm is selected as the light source. In this case, the depth of light penetration is on average 15 μm (shown by the dashed line), which is a suitable result (depth of the conduction band = depth of light penetration + diffusion. In general, the depth of the conduction band should be greater than the thickness of the skin layer for the conductor at a given frequency of the device ( determined taking into account the conductivity of the conductor)).

Further in FIG. Figure 6 shows the results of modeling the concentration of carriers in the bulk of the photoconductive material. The following parameters of the light source were selected: a light beam of 10 μm x 10 μm, a power of 10 mW, and a wavelength of 850 nm; and the following parameters of the photoconductive material: silicon, diffusion coefficient 29 cm ² / s, carrier lifetime 1 μs.

In yet another example shown in FIG. 7, an optically controlled switch based on the GCPW line is considered. The width of the signal conductor in the coplanar transmission line is set to 2 μm, the width of the gaps between the signal conductor and the earth conductors on both sides is set to 6 μm. That is, the total line width along with the gaps will be 14 microns. So that the signal conductor, when the switch is on, can short to ground, the size of the photoconductive section must exceed this total line width. We average the conductivity distribution in the illuminated region as follows: the maximum conductivity is 10,000 S / m in a section with a circular cross section with a diameter of 25 μm, the conductivity drops to 5,000 S / m in a section with a diameter of 50 μm (Fig. 7).

The simulation results of the S-parameters of the switch according to the present invention and the described conductivity distribution are presented in FIG. 8: as you can see, a broadband switch with isolation between the ON / OFF states of more than 20 dB was obtained, while in the OFF state, in which (as shown above with respect to Figs. 4A – 4B for the parallel type switch in Fig. 2B) the signal should completely pass to the output, the reflection coefficient is approximately –45 dB, and the transmission coefficient –0.03 dB, and in the ON state, in which the signal should be shorted, the reflection coefficient is approximately –0.95 dB, and the transmission coefficient –23 dB.

Thus, the present invention provides an optically controlled micron-sized switch for frequencies above 30 GHz with the possibility of using a micron-sized light source containing a semiconductor substrate with a photoconductive section and an integrated RF transmission line, while reducing stray capacitance and increasing the accuracy and density of components. In other words, the following technical result is provided:

- reducing the size (miniaturization) of the switch, and as a result, reducing spurious losses,

- low dielectric loss at the substrate of the transmission line and the high quality of manufacture of conductors in the transmission line, and as a result, a reduction in insertion loss in the EHF range,

- reducing power consumption, improving isolation between ON / OFF states and increasing switching speed by reducing the switch, provided that acceptable levels of conductivity and carrier lifetime are achieved,

- increase in the working frequency band,

- Easy integration into SoI and CMOS devices.

Hereinafter, other embodiments of the present invention will be described herein. It should be understood that the invention is not limited to these options, and specialists in this field will be able to get other options for implementation, guided by the principles set forth here to create a high-frequency switch.

So, for example, not only a microstrip line (Fig. 2A) and a coplanar waveguide with an earth layer GCPW (Fig. 2B), but also a conventional coplanar waveguide (CPW), without an additional earth layer, as shown in FIG. 9A, or any other suitable transmission line. A variant is also possible in which the semiconductor substrate serves directly as the dielectric layer for the coplanar line, and then the connection layer and the ground layer are not required. The shape of the hole for the passage of light from the light source to the photoconductive section can be any - both round, as mentioned earlier, and square, as shown in FIG. 9B, both rectangular and any other, provided that its size allows the light to freely reach the photoconductive section. The structure of the ground layer is also not limited to the present invention and can be selected in any convenient configuration — solid, as mentioned above, or mesh, as shown in FIG. 9C.

The thickness of the semiconductor substrate in structures where it is necessary to shorten the conductors of the transmission line in a horizontal plane should be greater than or approximately equal to the depth of light absorption at the working wavelength of the light source, taking into account the diffusion length of the charge carriers on the photoconductive section of the semiconductor substrate.

As for implementations on the coplanar line (CPW, GCPW), in FIG. 10A shows an embodiment in which a rectilinear solid signal conductor is used. This option is sufficiently effective and has all of the above advantages of the present invention. However, the implementation of the signal conductor with additional heterogeneity 16 (Fig. 10B) can provide a stronger reflection of the signal from the photoconductive section 11 due to the increase in the area of the switching zone (decrease in shunt resistance). In addition, the implementation of the signal conductor in the form of a grid (Fig. 10C) can provide better excitation of carriers in the photoconductive section while maintaining the quality of signal transmission.

Another option for the transmission line may be a SIW line (substrate integrated waveguide, pinwave waveguide) shown in FIG. 11A – 11D. In such an embodiment, a dielectric-filled waveguide is formed: the upper (4) and lower (17) walls of the waveguide are metallized surfaces of the semiconductor substrate 1 itself. In this case, there must be a hole 12 (or several) in the upper metallization layer 4 for light to pass from source (s). The side walls are formed by rows of transition metallized holes 18, made, for example, according to TSV (Through Silicon VIA) technologies. The step between the holes should be less than λ / 10, where λ is the working wavelength of the device.

The thickness of the semiconductor substrate (wafer) in such a structure, since it requires shorting the conductors of the transmission line in a vertical plane, should be approximately equal to the depth of light absorption at the working wavelength of the light source, taking into account the diffusion length of the charge carriers on the photoconductive section of the semiconductor substrate (or not exceed her).

In the off state (with the light source turned off), the signal will pass freely in the implemented waveguide (Fig. 11A, 11C). When the light source is turned on, it will be reflected from the activated conduction band (Fig. 11B, 11D).

To improve the locking efficiency of the SIW line, several light sources can be used that form a reflecting wall in the waveguide, as shown in FIG. 12.

When using the VCSEL grating, it is possible to create a structure without the need for VIA, in which the waveguide SIW line will be formed directly by the illuminated (activated) sections 11 of the photoconductor forming the side walls of the waveguide (Fig. 13A). 13A only activated photoconductive sections 11 are shown, but it should be understood that in this structure there may also be non-activated photoconductive sections under corresponding non-light emitting light through windows 12.

In the extreme case, it can be a fully reconfigurable switching structure in which the signal 14 can be sent to any desired point on the device (Fig. 13B) and which can also be used for dividing / adding power, phase shifters, and other passive RF structures.

In FIG. 14 shows a top view of an example implementation of a phase shifter in which the proposed optically controlled serial switches are used. On the semiconductor substrate 1, segments 19 of the transmission line are made, which are the branches of the phase shifter that provide the necessary phase delays when the signal passes through them. Between the segments, gaps were made with a length comparable to the width of these segments, and in the region of these gaps there are photoconductive sections 11 of a corresponding size onto which light can be emitted from vertically emitting lasers located above them.

In the case when the substrate as a whole has a large carrier lifetime, it is proposed to use a local (within the required regions) decrease in the lifetime of free carriers in a semiconductor, for example, directly in the process of manufacturing the semiconductor substrate by introducing new recombination centers in silicon. Several approaches are possible: ion implantation, electron beam irradiation, and others. This still allows the use of a relatively wide variety of materials as substrates, but eliminates the need for separate photoconductive elements and their installation in the substrate. If necessary, such a treatment can be completely subjected to the entire substrate.

In FIG. 15 shows an example of such local processing when, on the silicon substrate of the phase shifter mentioned previously with reference to FIG. 11 (and in the General case, on the substrate of any desired device containing the proposed switches), in the areas where the photoconductive sections should be located (shown by a circle), an ion bombardment is performed. Accordingly, in these areas, the lifetime of free carriers decreases, and photoconductive regions with the required characteristics are formed.

In the case where the entire substrate has a photoconductivity effect, the density of the arrangement of elements is determined by the photoconductivity zone, i.e. the sum of the aperture size of the light source and the diffusion length. The distance between adjacent switches is recommended to be set large by at least one more diffusion length. At the periphery, the conductivity decreases exponentially.

A different situation is also possible. In the case where the substrate as a whole has the necessary carrier lifetime, it is possible to further limit the photoconductive regions. To do this, borders are created around the photoconductive sites at which the carriers recombine very quickly. The processing methods are the same: ion implantation, electron beam irradiation, and others. This allows you to increase the packing density of the elements on the substrate, which is already made of a material suitable for use directly as a photoconductive section.

In FIG. 16 shows an example of such local processing when, on the silicon substrate of the phase shifter mentioned previously with reference to FIG. 14, an ion bombardment is carried out at the boundaries of the regions where the photoconductive regions (shown by a small square) should be located. Accordingly, at these boundaries, the lifetime of free carriers decreases sharply, the carriers recombine very quickly, and thereby create boundaries within which photoconductive regions with the required characteristics still remain.

It should be understood that this document shows the construction principle and basic examples of an optically controlled mm-range switch based on a semiconductor substrate. A person skilled in the art, using these principles, will be able to obtain other embodiments of the invention without creative efforts.

Application

Optically controlled switches based on photoconductive elements and a semiconductor substrate, created using them strip lines, circulators, phase shifters, switches and antennas with adaptive beamforming according to the present invention can be used in electronic devices that require RF signal control, for example, in the millimeter range for mobile networks of promising standards 5G, 6G and WiGig, for various sensors, for Wi-Fi networks, for wireless Chi energy, including long distance, systems of "smart home" and other adaptive to the mm-range of intelligent systems for car navigation, for the Internet of Things (IoT), wireless charging, etc.

It should be understood that although in this document to describe various elements, components, areas, layers and / or sections, terms such as "first", "second", "third" and the like can be used, these elements, components , areas, layers and / or sections should not be limited to these terms. These terms are used only to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section may be called a second element, component, region, layer or section without departing from the scope of the present invention. In the present description, the term "and / or" includes any and all combinations of one or more of the corresponding items listed. The elements mentioned in the singular do not exclude the plurality of elements, unless specifically indicated otherwise.

The functionality of the element indicated in the description or claims as a single element can be implemented in practice through several components of the device, and vice versa, the functionality of the elements indicated in the description or claims as several separate elements can be implemented in practice through a single component.

In one embodiment, the elements / blocks of the proposed optically controlled switch are located in a common housing, are located on the same frame / structure / substrate / printed circuit board and are structurally connected to each other by means of assembly (assembly) operations and functionally by means of communication lines. The mentioned communication lines or channels, unless otherwise indicated, are standard communication lines known to specialists, the material implementation of which does not require creative efforts. A communication line can be a wire, a set of wires, a bus, a track, a wireless communication line (inductive, radio frequency, infrared, ultrasonic, etc.). Communication protocols over communication lines are known to specialists and are not disclosed separately.

The functional connection of elements should be understood as a connection that ensures the correct interaction of these elements with each other and the implementation of one or another functionality of the elements. Particular examples of functional communication may be communication with the possibility of exchanging information, communication with the possibility of transmitting electric current, communication with the possibility of transmitting mechanical motion, communication with the possibility of transmitting light, sound, electromagnetic or mechanical vibrations, etc. The specific type of functional connection is determined by the nature of the interaction of the mentioned elements, and, unless otherwise indicated, is provided by well-known means using principles well known in the art.

The design of the elements of the proposed device is known to specialists in this field of technology and is not described separately in this document, unless otherwise indicated. The elements of the device may be made of any suitable material. These components can be made using known methods, including, by way of example only, machining on machines, investment casting, and crystal growth. Assembly, connection and other operations in accordance with the above description also correspond to the knowledge of a person skilled in the art and, therefore, will not be explained in more detail here.

Although exemplary embodiments have been described in detail and shown in the accompanying drawings, it should be understood that such embodiments are merely illustrative and not intended to limit the present invention, and that the present invention should not be limited to the particular arrangements and constructions shown and described, since In the art, based on the information set forth in the description and knowledge of the prior art, various other modifications may be apparent in Rianta of the invention without departing from the spirit and scope of the invention.

Claims (45)

1. Optically controlled switch, containing from bottom to top: a substrate made of a semiconductor material, which in the absence of external influences acts as a dielectric, a first conductive layer of the transmission line made of conductive material on the upper side of the substrate, and bottom-up laser: lower distributed Bragg reflector (DBR) of the laser, made partially translucent to allow laser light emission through the lower DBR, active area of the laser, and upper DBR laser, made completely reflective, moreover, in the substrate in the zone of incidence of the beam is made a photoconductive section, which when illuminated with light is in the state of the conductor, and in the absence of light is in the state of the dielectric in the first conductive layer of the transmission line in the area of incidence of the beam, at least one radiation window is made to allow the passage of laser light to the photoconductive section. 2. The optically controlled switch according to claim 1, wherein the substrate is made of highly resistive photoconductive material. 3. The optically controlled switch according to claim 1, wherein the transmission line is a coplanar waveguide (CPW), moreover, the first conductive layer contains a coplanar line containing a central signal conductor passing over the photoconductive section and the semi-infinite earth conductors surrounding it, moreover, the dielectric layer for CPW is said substrate. 4. The optically controlled switch according to claim 1, further comprising: a connecting layer made of a translucent dielectric between the first conductive layer and the lower DBR. 5. The optically controlled switch according to claim 4, wherein the connecting layer is made of a dielectric film. 6. The optically controlled switch according to claim 4, wherein the transmission line is a coplanar waveguide (CPW), moreover, the first conductive layer contains a coplanar line containing a central signal conductor passing over the photoconductive section and the semi-infinite earth conductors surrounding it, moreover, the dielectric layer for CPW is the connecting layer. 7. An optically controlled switch according to claim 4, further comprising: a second conductive layer made of conductive material between the connecting layer and the lower DBR, moreover, in the second conductive layer of the transmission line in the zone of incidence of the beam made at least one radiation window to ensure the passage of laser light to the photoconductive section, wherein the first conductive layer is a signal layer of a transmission line, and the second conductive layer is an earth layer of a transmission line. 8. The optically controlled switch according to claim 7, in which the transmission line is a coplanar ground-layer waveguide (GCPW), moreover, the signal layer contains a coplanar line containing the central signal conductor passing over the photoconductive section and the semi-infinite earth conductors surrounding it. 9. The optically controlled switch according to claim 7, in which the transmission line is a microstrip line, moreover, the signal layer contains two segments of the microstrip line, separated by a photoconductive section. 10. An optically controlled switch according to claim 1, further comprising: a second conductive layer made of conductive material on the lower side of the substrate, moreover, the transmission line is a waveguide with pin walls (SIW), moreover, the first conductive layer is the upper wall of the SIW, and the second conductive layer is the lower wall of the SIW, moreover, the dielectric layer for SIW is said substrate. 11. An optically controlled switch according to claim 10, further comprising: side walls formed by rows of transition metallized holes (VIA) made in the substrate between the first and second conductive layers on opposite sides of the photoconductive section. 12. An optically controlled switch according to claim 11, further comprising: at least one additional laser and at least one additional photoconductive portion corresponding thereto located adjacent to said laser and said photoconductive portion between the side walls of the SIW to form a reflective wall. 13. An optically controlled switch according to claim 1, further comprising: a connecting film made between the active region of the laser and the lower DBR. 14. The optically controlled switch according to claim 1, wherein the thickness of the substrate is equal to the depth of light absorption at the working laser wavelength, taking into account the diffusion length of the charge carriers in the photoconductive section. 15. The optically controlled switch according to claim 1, in which the width of the conductors in the first conductive layer, the size of the laser aperture and the diffusion length of the charge carriers in the photoconductive section are of the same order. 16. The optically controlled switch according to claim 1, wherein the photoconductive section is made in the substrate using the method of introducing new recombination centers into the semiconductor. 17. The optically controlled switch according to claim 16, wherein the substrate as a whole has a carrier lifetime of free carriers in the semiconductor exceeding the carrier lifetime required to form a photoconductive section with predetermined characteristics, and the photoconductive section is made in the substrate using the method of introducing into the semiconductor new centers of recombination in the zone of incidence of the beam. 18. The optically controlled switch according to claim 16, in which the substrate as a whole has a lifetime of free carriers in the semiconductor equal to or less than the lifetime of the carriers required to form a photoconductive section with predetermined characteristics, and the photoconductive section is made in the substrate using a method for introducing new recombination centers into the semiconductor along the boundary around the beam incidence zone. 19. A high-frequency switching device containing a plurality of optically controlled switches according to claim 1, made on the basis of a single substrate and containing interconnected transmission lines. 20. A reconfigurable optically-controlled switch containing an array of optically-controlled switches according to claim 10, made on the basis of a single substrate, in which at least a portion of the adjacent optically-controlled switches are configured to form side walls SIW when turned on .

Images