DE3148968A1 - CAPACITOR WITH CHANGEABLE CAPACITY - Google Patents

Description

3 U 896

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Variable capacitance capacitor

The invention relates to a capacitor with variable capacitance, which is constructed so that the change in its capacitance can be controlled over a wide range with great accuracy.
5

It is known as a variable capacitance capacitor to use a PN junction element as shown in FIG. In Fig. 1 are a semiconductor region 1 of the N conductivity type, a semiconductor region 2 *.

of the P conductivity type, a PN junction 3, ohmic electrodes 4 and 5, which are respectively arranged on the areas 1 and 2, lead-out connections or output conductors 6 and 7, which are provided for electrodes 4 and 5, and a depletion layer 8 is shown. In the case of a capacitor with variable capacitance, the one described above The depletion layer 8 is built up as a function of the bias voltage applied to the output conductors 6 and 7 expanded and contracted, the change in capacitance due to expansion or contraction the depletion layer 8 between the output conductors 6 and 7 is removable.

A conventional or known variable capacitance capacitor incorporating the elements described above Uses PN junction, but has the following disadvantages:

1. Since the dependence of the capacity of the depletion layer is used by the bias in the PN junction, the smallest possible capacity depends on the concentration of the imperfections in the semiconductor areas, while the greatest possible capacity from the increase in the conductive

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Component depends. It is thus practically impossible for a large change in capacity to occur great Q-value and due to the fact that the change in the Q-value comes with a change the capacity is larger, difficulties arise in the design of the circuits.

■ 2 "Since the bias to change the capacitance to the common output conductor is placed and the change in capacitance on the common output conductors is removed when using the known capacitors with variable capacitance in a resonance circuit or the like, the input signal voltage itself has an unnecessary change in capacitance cause, which leads to an impairment of the signal. There is also a special circuit structure is necessary to make the interaction between the input signal voltage and the bias voltage as small as to keep possible, such known capacitors with variable capacitance can only to a limited extent Scope can be used.

ο The concentration of the imperfections in the semiconductor areas is controlled via a diffusion process or via ion implantation to increase the capacity of the To determine the depletion layer. However, since such processes are generally only a low one Can have use and usefulness effects conventional capacitors with variable capacitance not in practice in the form of integrated circuits be formed.

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It has therefore been proposed to provide variable capacitance capacitors which do not use PN junction elements *. Fig. 2 shows in a circuit diagram the basic structure of such a capacitor with variable capacitance. In Fig. 2, fixed capacitive elements C ₁ to C are respectively representing the variable capacitance C_ of the circuit, switching elements S ₁ to S respectively, and capacitance take-off terminals 6A and 7A, η is a selected integer.

In the arrangement shown in FIG. 2, it is assumed that the switching elements S to S can be opened and closed independently, so that the sum of the capacitance (the variable capacitance C _Q can be chosen arbitrarily *) of the fixed capacitive elements C to C _{n is} equal to C _T. It is therefore C = C. + C ₂ + C ₃ + .... + C. The circuit shown in FIG. 2 thus allows the capacitance to be changed in the range from C_ to C _n + C _T by opening and closing the switching elements S ₁ to S in a suitable manner.

Variable capacitance capacitors are generally used in resonance circuits, tuning circuits, fceit constant circuits etc. related. There are, however many uses that do not require a fully continuous change in capacity. In a tuning circuit, for example a her-. conventional commercial radio receiver, it is sufficient to that the capacity is changed in a number of steps according to the number of transmitter channels. on this area is never a completely stepless one Change required.

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By dimensioning the fixed capacitive elements in such a way, that they have different capacities, the capacity can be changed roughly and finely. It is therefore possible to change the capacity over a wide range with a relatively small number of fixed to control capacitive elements with great accuracy.

Finally, when discrete capacitors are used as the fixed capacitive elements C ₁ to C, these capacitors must be high-precision components which are selected under careful examination in order to change the capacitance with high accuracy. To do this, however, • it is necessary to select, from a large number of individual capacitors, those that have the specified characteristics or parameters at great expense. This leads to higher production costs due to the reduced usable percentage, so that the known capacitors with variable capacitance do not meet the practical requirements in this field of technology.

The invention is therefore primarily intended to address the above-mentioned disadvantages of the known capacitors with variable capacitance be eliminated by creating a variable capacitance capacitor in which a number of fixed capacitive Elements is formed on a common substrate.

3 shows in a perspective view the basic structure of the variable capacitor according to the invention Capacity. The structure of the variable capacitance capacitor in FIG. 3 is in the form of that shown in FIG Circuit with η equal to 5-. The substrate of this capacitor with variable capacitance is an insulating layer 9, on the surface of which a desired metal is evaporated,

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whereupon several conductive layers 10 _A to 10 ″ are subsequently formed using a photo-etching process.

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Finally, an insulating layer 11 is formed in such a way that that it covers most of the conductive layers 10 to 10 ". A common conductive layer 12 is then placed on the surface of the insulating layer

11 formed.

The conductive layers 10 are formed by having a desired dielectric material on top of the Most of the surface area is vapor-deposited or by means of a chemical vapor-deposition process using A mask is applied. It is also possible after applying the dielectric material the substrate to remove the unnecessary parts by a photo-etching process in order to create these conductive layers to create. The common conductive layer 12 is formed by vapor deposition of a desired metal. Subsequent to the above work steps, each layer of the number of conductive layers 10,. until 10"

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wired to the switching elements S ₁ to S ₅ (W ₁ to W ₅ ). In Fig. 3, t denotes the thickness of the insulating layer 11, b the width of the common conductive layer 12 and I ₁ to I ₅ the contact length (overlap distance) of the conductive layers 10 ,. up to 10 "with the insulating layer 11.

In the illustrated in Fig. 3 structure, the conductive layers 10 form, to 10 ", the insulating layer 11 and the common conductive layer 12 along a plurality of capacitive elements, wherein the conductive layers 10 _A to 10 _£ than one electrode of each capacitive elements act while the common conductive layer

12 acts as the other electrode, which is capacitive for all.

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Elements is common. In this way, the capacitive elements C ₁ to C _{5 are} thus integrated on the substrate 9.

As for the capacitance of the capacitive elements C. to Cc, which are integrally formed on the substrate in this way, is the n-th capacitance V given as;

V _n = £ ° b ° l _n / t in Farads,
10

where S is the dielectric constant.

By using the conventional film formation process and photo etching process, the thickness t and the contact length 1 of the insulating layer 11 as well as the Width b of the common conductive layer 12 can each be controlled to a desired value, which makes it possible ? light to reduce the difference between the elements or products to a negligible level. It is still possible, the contact length 1 of the insulating layer 11 to a desired and wide range for each capacitive To interpret the element. In addition to this advantage, the technology of integrated circuits can be used, to measure the capacity of each capacitive element precisely =

By forming the switching elements in an integrated form on the substrate on which the capacitive elements are formed it is still possible to see capacitors to create with variable capacity? the one lesser Are large and can be manufactured at a lower cost.

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In the following, preferred exemplary embodiments of the invention are described in more detail with reference to the accompanying drawings explained:

Fig.

Figure 12 shows a cross-sectional view of a known variable capacitance capacitor.

Fig. 2 shows the basic structure in a circuit diagram

of the known variable capacitance capacitor shown in FIG.

Fig. 3 shows in a perspective view the basic structure of an embodiment of the inventive capacitor with variable capacitance.

Figs. 4, 8, 10 and the like.

show further embodiments of the invention.

Figs. 5, 6, 9 and

show the circuit diagrams of the exemplary embodiments of the invention.

Fig.

13a / b and c and Fig.

shows the characteristic diagram of an embodiment of the invention.

show sectional views and a perspective view of further exemplary embodiments the invention.

In Fig. 4, an embodiment of the invention is shown in which a plurality of capacitive elements and switching elements are formed in integrated form on a common substrate, wherein the switching elements consist of diodes. The substrate is a semiconductor substrate 13, the

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is heat-treated in an acidic atmosphere at a high temperature to form an insulating oxide film 12 on the surface of the substrate 13. Then part of the insulating film 14 is through Photo etching removed. A desired type of storage location that capable of providing P or N conductivity is selectively incorporated into the semiconductor substrate 13 from that described above Part diffused from where the insulating film is removed so that a variety of diodes D. to D ^ (PN diodes) is formed.

Then a plurality of conductive layers 10 to 10 ″, each with a region of each diode D ₁ to D ₆ . are to be connected, and a common conductive layer 15 is formed, which is to be connected together with the other area of the diodes. Thin resistance layers R ^ to R ₁ - are then formed in such a way that they cover part of the number of conductive layers 10 to 10_. This is followed by an insulating layer

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11 and a common conductive layer 12 are produced in a manner similar to the method shown in FIG. 3. The conductive layers 10 to 10, the common conductive layers 12 and 15, and the insulating layer 11 are formed by a suitable combination of a conventional vapor deposition method and a photo-etching method, as shown in FIG. In Fig. 4, V denotes the bias voltage. This bias voltage V "is applied to the capacitive elements via the lead wires W-, to W, which are connected to the thin resistance layers R., and R ₁ . and the bias voltage applying switches SW- to SWj. are connected.

In the illustrated structure of the capacitor with variable capacitance, the PN diodes D. to D ₁ . about the multitude

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of the conductive layers 10 _A to 10 _E rait each of the plurality of capacitive elements C ₁ to C ₁ . which are formed by the plurality of conductive layers 10 to 10, the insulating layer 11 and the common conductive layer 12, the diodes acting as switching elements S .. to Sr in FIG. 5 shows the equivalent circuit diagram with a single capacitive element C. and a single switching element S ₁ . When the switch SW ₁ applying the bias is opened, there is no bias V _D on the capacitive element C ₁ and on the diode D ₁ , whose AC resistance will be greater, so that a small capacitance between the terminals 6 _a and 7 _{Λ is} removed. If then the switch SW. is closed, the bias voltage V _{ß is applied to} the capacitive element C ₁ and the diode D _{1 is} biased in the forward direction, so that a direct bias current fHessen is. The alternating current resistance of the diode D ₁ is therefore small, which has the consequence that the capacitance of the capacitive element C ₁ in the form of a layer structure of a conductive layer 10 _Λ , the insulating layer 11 and the common conductive layer 12 between the terminals 6, and 7 is removed.

Since the other capacitive elements C- to C _{5 are connected in} parallel with the capacitive element C ₁ , the capacitance actually removed between the terminals 6 _Λ and 7 can be changed in a wide range by switching _{the corresponding biasing switch SW 2 .bis} SWc can be closed or opened. It is of course evident that the number of capacitive elements is not limited to 5 and can be freely selected. It should be pointed out that the thin resistance _{layers R 1} to R ₅ are provided for defining the direct bias current through the diodes D ₁ to D ₅ and an alternating voltage 35

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to block part of the input voltage signal between the capacitance pick-up connections 6 and 7 is present.

. In the case of an AC voltage input signal with a large amplitude, the signal with a large amplitude will cause the diodes to block and switch through, so that the capacitor with variable capacitance may work incorrectly. To avoid this, a source of _{reverse bias voltage V 0 is} provided, as shown in FIG.

6, to attach more and a reverse bias voltage to the capacitive elements C, through C _5. In this case, when using the bias switches SW ₁ to SW ₅ with two switch contacts, it is possible to select the bias or the bias in the reverse direction, depending on the situation.

In the foregoing, an embodiment was described in which PN diodes are used as diodes, but diodes of other suitable types can also be used. For example, diodes made from an intrinsic semiconductor can be used as the semiconductor substrate, so-called PIN diodes. Furthermore, Schottky diodes having a Schottky barrier layer between the semiconductor substrate and a desired metal bonded to the semiconductor substrate can be used. When using Schottky diodes, a selected metal can be used on the surface of the semiconductor substrate by vapor deposition or a similar method _/ instead of diffusing impurities in order to form a PN diode, as is shown in FIG.

In the exemplary embodiments described above, the diodes act as switching elements by making a difference in the size of the alternating current resistance when applied

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a bias voltage V = V _ß and without a bias voltage V = V. in the voltage V (horizontal axis) versus current I (vertical axis) characteristic of the diodes, as shown in FIG. The diodes used according to the invention are therefore not restricted to diodes with a specific structure.

8 shows another exemplary embodiment of the invention, in which surface transistors are used as switching elements. In FIG. 8, the same or similar components or components as in FIG. 4 are provided with the same reference numerals. Surface transistors TR ₁ to TR ₅ , for example NPN transistors, are provided, the collectors of which are connected to the conductive layers 1CL to 10 ", the emitters of which are connected to the common conductive layer 15 and their bases to the thin resistance layers R ₁ to Rc - each connected.

These junction transistors TR ₁ to TR ₅ can be formed in that, in addition to the method of generating PN diodes, as shown in FIG. 4, an impurity diffusion takes place.

The conductive layers 1O ₇ . to 10 ", the insulating layer 11, the common conductive layers 12 and 15, the thin resistance layers R ₁ to R ₅ and the lead wires W _{1 to W 1n} can be provided in the same manner,. as shown in FIG.

In the case of a capacitor with variable capacitance of the structure described above, a plurality of capacitive elements C ₁ to C ₅ made up of a plurality of conductive layers 10,. to 10p, an insulating layer 11 and a common conductive layer 12, _{junction transistors TR 1} to TR ₅ over the plurality of conductive layers 10j. up to 10-, connected,

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wherein the transistors as switching elements Sj to S _n . to serve. Fig. 9 shows the equivalent circuit diagram with a capacitive element C ₁ and a switching element S-. When the switch SW ^ applying the bias voltage is open, there is no bias voltage V_ at the base B of the junction transistor TR-, which thus blocks. At this point in time, the alternating current resistance between the collector C and the emitter E is so great that only the remaining capacitance between the collector C and the emitter E of the transistor TR ^ is taken as capacitance between the connection conductors 6- and 7. This residual capacity can be reduced considerably.

When the switch SW- applying the bias voltage is closed, a bias voltage V _β is applied to the base B of the junction transistor “TR-, so that a direct bias current flows between the base B and the emitter E”. At this point, the alternating current resistance between the collector C and the emitter E becomes very small, so that the capacitance of the element C-, between the connecting conductors.

6 _rows and 7 _{n is} decreased. By switching the other bias voltage switches SW2 to SW ₁ on and off, the capacitance between the connecting conductors 6 ^ and 7th can be changed over a wide range, which includes the capacitances of the other capacitive elements C ₂ to C ₅ .

The thin resistance _{layers R 1} to Rg are provided for the purpose of specifying the direct bias current through the bases of the junction transistors TR to TR ₅ .

10 shows a further exemplary embodiment of the invention in which field effect transistors are used as switching elements. 4, 8 and 10, the same components or components are provided with the same reference numerals. The field effect transistors FTR ₁ to FTRj-, which are for example MOS transistors, have their drains on the conductive layers 10 to 10, respectively. are with their sources

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are connected to the common conductive layer 12 and their gates are connected to the switches SW ₁ to SW ₁ which apply the bias voltage - via lead wires W _g to W ₁₀ .
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These MOS transistors FTR. to FTRt- can be formed by creating two regions for drain and source at the same time with impurity diffusion in the formation of PN diodes. A conductive layer for the gates is designated by 16. This layer is formed on the thin insulating oxide layer 14 between the drain and source and can be produced at the same time as the conductive layers 10 _& 10 and the common layer 15 are formed. The conductive layers 10 _Å to 10_, 15 and 12, the insulating layer 11 and the lead wires W to Wg _1Q can be provided in the same manner as shown in Fig. 4.

In a capacitor having variable capacitance of the structure described above are connected to the plurality of capacitive elements C ₁ to C _5, which consist of a plurality of conductive layers 10 to 10, an insulating layer and the common conductive layer 12, the MOS transistors FTR ₁ to FTR ₅ via the plurality of conductive layers 10,. connected to 1-0_, where the

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Transistors serve as the switching elements S ₁ to Sr shown in FIG. 2. Fig. 11 shows the equivalent circuit diagram of a capacitive element C ₁ and a switching element S-]. When the switch SW ₁ applying the bias voltage is open, there is no bias voltage V at the gate G of the MOS transistor FTR ₁ , which in turn blocks, so that the AC resistance between the drain D and the source S becomes greater. It is only the remaining capacity

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-In the meantime, drain D and source S of transistor FTR _{1 are} disconnected as capacitance between connection terminals 6 'and 7-

n A

took. This residual capacity can be reduced considerably.
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When the bias switch SW "^ is closed, the bias voltage V _{n is applied to} the gate G of the MOS tran-

sistor FTR ₁ , so that a channel is formed between drain D and source S of transistor FTR .. and thus the AC resistance between drain D and source S is much smaller. The capacitance of the capacitive element C, between drain D and source S can therefore be tapped. By opening and closing the other switches SW ₁ to SW ₅ which apply the bias voltage, the capacitance between the connecting _{conductors 6 A} and 7 can be changed over a wide range, which includes the capacities of the other capacitive elements C ~ to Cc. In this way, field effect transistors can be used instead of the MOS transistors. These junction transistors can be formed in that an impurity diffusion occurs during the manufacture of the PN diodes in FIG. 4 or the junction transistors in FIG.

Fig. 12 shows another embodiment of the invention in which photoconductive elements serve as switching elements. In Fig. 12, similar parts or elements as in Figs. 4, 8 and 10 are provided with the same reference numerals. Photoconductive elements PT. to PT ₅ are with one side on the conductive layers 10-. to 1Q ″ respectively, while their other sides are connected to the common conductive layer 15. In the embodiment shown in FIG. 12, an insulating layer 9 serves as the substrate, with a photographic layer on a part of the surface of the substrate.

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conductive film, for example made of cadmium sulfide CdS, is vapor-deposited and shaped. Each conductive layer 10 to 10 ″ is connected to one side of the photoconductive film, while the other side is connected to the common conductive layer 15, so that the photoconductive elements PT ₁ to PT ₅ result. The conductive layers 10 _A to 10 and 15 and the insulating layer 11 may be provided in the same manner as shown in Fig. 3. There are also light shutters 16 and 17, which can be moved in the direction of the arrows, and a light source 18 and an energy source 19 are provided.

In a capacitor with variable capacitance of the structure described above _{, photoconductive elements PT 1 are associated with the plurality of capacitive elements C 1} to C ₅ , which consist of the plurality of conductive layers 10 to 10 ″, the insulating layer 11 and the common conductive layer 12 to PT ₅ connected via the plurality of conductive layers 10 _Λ to 10, the photoconductive

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Elements serve as switching elements S ₁ to S ₅ in Fig. 2. When light is irradiated on the photoconductive films that the photoconductive elements PT ₁ . to form PT ₅ , a current flows through these films, so that their resistance decreases noticeably. The photoconductive elements can therefore be used as a resistance change switch. Because the position on which the light from the light source 18 falls is set via the light screen 16, it is thus possible to selectively actuate the photoconductive elements as switching elements. If the light shutter 16 is set so that the light falls on, for example, the photoconductive elements PT. To PT ₃ , as shown in FIG. 12, only the photoconductive elements

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Elements PT ₁ to PT-. a low resistance value. This state corresponds to the closing or switching on of the switching elements. The total capacitance C. + C- + C _{3 of} the capacitive elements C ₁ to C ,, which are connected in parallel can therefore be obtained between the connection conductors 6 and 7_. Since no light falls on the other photoconductive elements PT ^ and PT ₅ at this time, their high resistance value is retained, which corresponds to switching off or opening the switching elements, so that no capacitance of the capacitive elements C. and C- is retained on the connecting conductors can.

In working conditions in which the resistance component of the photoconductive elements PT to PT _{3 is} smaller than the impedance of the capacitive elements C ₁ to C ₃ , the Q factor is large in this embodiment, so that these capacitive elements can work like ordinary capacitive elements .

In the embodiments described above, an integrated capacitor could be provided by • that together with capacitive elements on the same substrate, semiconductor switches were formed that consist of different semiconducting elements exist as switching elements, whereby the switching elements are designed in such a way that that they work as resistance change switches.

In the embodiments shown in FIGS. 4, 8 and 10, the insulating oxide film 14, which is on the Surface of the semiconductor substrate was formed, can be used as a dielectric, which is the capacitive element forms. In this way, the design of the capacitor could be simplified in an integrated form. In these . Cases consisted of the capacitive elements from the conductive layers 10 ,. up to 10 ", which are equipped with island areas

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are bound, and a layer structure of the insulating

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Oxide film 14 and the common conductive layer 12. The island region 20 was not mentioned in the description of the above exemplary embodiments. This area must however, in the manufacture of integrated circuits, there is an interaction in the characteristics with other generated elements to prevent. In this embodiment of the invention, the island area can be used as one end of the capacitive element as it is.

In Fig. 14 still another embodiment is the Invention shown in the capacitors VC with variable Capacitance that can be obtained according to the embodiments described above, formed in an integrated form on a substrate 13 are on the semiconductor integrated circuits IC as well are formed. Because with this arrangement the capacitors with variable capacitance in a single plate are built into an integrated circuit, additional connection conductors, usually from the outside need to be welded on are missing and superfluous likewise the work of connecting the connections, the product still having a smaller component size and a reduction in manufacturing cost can be achieved.

The capacity of the plurality of capacitive elements in the various ones described above Embodiments can be changed, i.e. weighted or measured, so to speak, by adding the contact area is changed between the number of conductive layers and the insulating layer that make up the conductive finishes covered. However, any other suitable measure or procedure can also be taken can be applied to change the surface area.

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With partially different thicknesses of the insulating layer or partially different structure of the insulating layer For example, the above can be achieved.

In the manufacture of the various semiconductor switches the conductivity type of the semiconductor areas can be freely selected to get voted.

From the above it can be seen that according to the invention it is possible to obtain a variable capacitance capacitor that does not use a PN junction by in integrated form on a common substrate a large number of fixed capacitive elements and a plurality of switching elements are formed, which are connected to the capacitive elements, respectively.

The formation according to the invention results in the following achieved:

1. As it is possible, the capacity of a smallest Value based on the variable capacity a circuit is determined, which can be set as desired, up to a maximum value freely and exactly to change that based on

of the electrode area can be determined, which can be adjusted as desired, the area of the The change in capacitance is considerably greater than with conventional capacitors with variable capacitance be. Thus, if the capacitor according to the invention with variable capacitance in a resonance circuit

or a tuning circuit is used, it is * possible to use an extraordinarily large range of changes the center frequency, which allows the circuit to be designed more freely.

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2. It is possible to provide a larger Q factor for the capacitance by using the switching element accordingly from »· and it is still possible to reduce the change in the Q value due to a change in capacitance.

3. Since the capacitance is changed by means of the switching elements, there is no significant change in the capacitance with an input signal, so that an impairment of the signal is avoided.

4. Since the technology of the formation of integrated circuits in the manufacture of the capacitors according to the invention with variable capacity is applicable *, the size of the products and the manufacturing costs be reduced.

5. Since the production of the inventive capacitive Elements no diffusion process or no ion implantation needed to control the impurity concentration, easily resulting in non-uniformity It is possible to eliminate the non-uniformity in capacitance from one capacitive element to another to keep them as small as possible, which increases the proportion of usable or usable components.

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Claims (8)

Patent attorneys Dipl.-Ing. .H; - ^ eickmä-nny Diril-pKYs. Dr. K. Fincke Dipl.-Ing. F. A. Weickmann, Dipl.-Chem. B. Huber Dr.-Ing. H. Liska 8000 MUNICH 86 J Q POST BOX 860 820 ' MDHLSTRASSE 22 TELEPHONE (089) 980352 TELEX 5 22 621 TELEGRAM PATENTWEICKMANN MUNICH FP-81-136 Clarion Co = "- Ltd. P / ht. 35-2 Hakusan 5-chome, Bunkyo-ku
Tokyo, Japan Variable capacitance capacitor PATENT CLAIMS [1 J capacitor with variable capacitance, characterized by a substrate (9), a plurality of conductive layers (10, to 10 ") formed on the substrate (9), an insulating layer (11)" formed in this way that it covers the conductive layers (1CL to 10 _E ), a common conductive layer (12) which is formed on the insulating layer (11), and switching elements (S-, to S ₁ -), on one side of each are connected to one of the plurality of conductive layers (10. to 10), while the other sides of the switching elements (S .. bis-Sr) are connected to a common point (7j,), so that a plurality of capacitive elements is formed, that of the multitude of senior officials Layers (10,. To 10_) and the plurality of switching elements A h> (S ₁ to S _n ). 2. Capacitor according to claim 1, g e k e η η - characterized by a substrate (9), a plurality of conductive layers (10. to 10 _E ) which are formed on a part of the substrate (9), an insulating layer (11) which is formed so that the conductive layers ( 10 to 10), a first joint A ti conductive layer (12) formed on the conductive layers (1O _2. to 10 "), switching elements (S ₁ to S ₁ -) formed on the other part of the substrate (9) and on one side with a the multitude of senior Layers (1O _7th to 10) are each connected, a second a hi - common conductive layer (15) which is connected to the switching elements (S ₁ to Sg) on their other sides, and a switching device to selectively _{excite the switching elements (S 1} to S _1. ), so that a plurality of capacitive elements are formed which corresponds to the plurality of conductive layers (1O _7. to 10 ") and switching elements (S ₁ to S, -). 3. Capacitor according to claim 2, characterized in that the size of the surface areas of the conductive layers (10 _A to 10_) are in contact is different. 4. Capacitor according to one of claims 2 and 3, characterized in that the substrate (9) consists of a semiconductor material. 5. Capacitor according to one of claims 2 to 4, characterized in that the switching elements (p. Ί to Sc) consist of semiconductor elements. "'■■' ^: - 3U8968 <> - j - 6th Capacitor according to Claim 5, characterized in that the semiconductor elements are PN diodes
(D ₁ to D ₅ ) are » 7 “capacitor according to claim 5, characterized in that the semiconductor elements Schottky diodes are. 8. Capacitor according to claim 5, characterized geke η η. shows that the semiconductor elements are junction transistors (TR ₁ to TR5). 9 “Capacitor according to claim 5, characterized in that the semiconductor elements are field effect transistors (FTR ₁ to FTR ₅ ). 10 _o capacitor according to claim 5, characterized in that the semiconductor elements are photoconductive elements (PT to PT ₅ ) and that a light projection device (16, 17, 18, 19) is provided to selectively
Light on the photoconductive elements (PT ₁ to PT ₅ )
project. 11 »capacitor according to claim 2, characterized in that g e k e η η, that the substrate (9) is part of a Forms semiconductor substrate for an integrated circuit.