RU2569906C1 - Multi-element mis varicap - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention can be used for development of varicaps intended for frequency and phase control of variable signal in wireless devices of HF and SHF ranges. MIS varicap comprises semiconductor of electron conduction type, dielectric, control electrode and drain unit of minority carriers with p-n area having depth equal to thickness of semiconductor. The drain source is made multi-element as a set of alternating areas of electron and hole conduction, at that one of the drain unit areas is coupled to the control electrode and linear size of the drain unit elements is equal to linear size of semiconductor.

EFFECT: decreased self-capacitance of the drain unit in inverse proportion to number of areas with hole conduction in elements of the drain unit thus leading to increased capacitance overlap.

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Description

The present invention relates to the field of semiconductor electronics and can be used to develop varicaps based on a metal-dielectric-semiconductor (MIS) system designed to control the frequency and phase of an alternating signal in RF and microwave radio devices.

Known MIS-varicap containing electronic conductivity semiconductor, dielectric, control electrode, drain node of minority carriers with a pn junction [Lloyd W Hackley, Seminole, Fla, "Varactor tuning diode with inversion layer, Put. 4.903.086, Feb. 20, 1990, US]. The disadvantage of this device design is the presence of the conductivity current of the pn junction, turned on in the forward direction, with the state of the device capacitance corresponding to the nominal value, which limits the possibility of its use as a capacitive key.

Closest to the proposed design is a MIS-varicap based on a metal-dielectric-semiconductor system [RF Patent No. 2486633, IPC H01L 29/92, publ. June 27, 2013]. This device contains a semiconductor of electronic conductivity, a dielectric, a control electrode and a drain assembly of minority carriers with a pn junction. The hole conduction region of the pn junction of the minority carrier sink node has a depth equal to the thickness of the semiconductor and is made in the form of a cylindrical layer, inside of which there is a part of the initial electron conductivity semiconductor connected to the control electrode.

A disadvantage of the known design of the device is the high value of the intrinsic capacitance of the elements of the drain node of minority carriers, limiting the amount of overlap in capacitance.

The objective of the proposed technical solution is to reduce the intrinsic capacity of the elements of the drain node of minority charge carriers, which will increase the ratio of the maximum capacity of the MIS-varicap to its minimum value.

The problem is achieved in that the MIS varicap contains an electronic type of conductivity semiconductor, a dielectric, a control electrode and a minority carrier drain node with a pn junction, the depth of which is equal to the thickness of the semiconductor, the linear dimensions of the pn junction along the surface are equal to the linear size of the semiconductor. The minority carrier drain node is made multi-element in the form of a set of alternating isolated regions of hole and electronic conductivity types with a depth equal to the thickness of the semiconductor, while one of the regions of the electronic conductivity type is connected to the control electrode.

In FIG. 1 and 2 show the design of the proposed multi-element varicap (in section and top view), FIG. 3 is its equivalent circuit.

The device contains an electronic conductivity semiconductor 1, a dielectric 2, a control electrode 3, a contact to a semiconductor 4. The minority carrier drainage unit contains electronic conductivity regions 5 (5a, 5c, 5c) and hole conduction regions 6 (6a, 6c, 6c), the depth which is equal to the thickness of the semiconductor, as well as the auxiliary dielectric 7. One of the elements of the drain assembly - 5v is connected to the control electrode 3 (Fig. 1). The linear dimensions of the elements of the drain node along the surface are equal to the linear size of the semiconductor (Fig. 2).

On the equivalent circuit: C ₀ is the specific capacitance of the dielectric, C _sc is the capacitance of the space charge region of the semiconductor, Rs is the equivalent series resistance of the device. The symbol D ₁ denotes the equivalent n-p-junction in the circuit between the electrodes 3 and 4, which is a system of series-connected n-p-junctions. In this case, one of the n regions of this chain is in contact with the control electrode 3. Correspondingly, the D ₂ is a pn junction equivalent to a system of pn regions connected in series between electrodes 3 and 4, and the region of the semiconductor 1 that is extreme in this diode chain is. The element C ₁ in the diagram is the equivalent parallel capacitance of the diode D ₁ , the symbol C ₂ denotes the equivalent parallel capacitance of the diode D ₂ .

The principle of operation of the proposed device is as follows.

When a positive voltage is applied to the control electrode 3 in the near-surface region of semiconductor 1, the enrichment regime with the main charge carriers and the device capacity are realized

C _H = C ₀ S,

where C _H is the nominal value of the capacity of the device;

With ₀ - the specific capacity of the dielectric 2;

S is the area of the control electrode 3.

In this case, the pn junction D _{1 is} switched in the opposite direction, and the pn junction D ₂ is in the forward direction, and the conduction current through the device is determined by the reverse current of the diode D ₁ , which makes it possible to use the device as one of the states of the capacitive switch for by increasing the overlap in capacity.

When a negative bias voltage is applied to the control electrode, the diode D _{1 is} turned on in the forward direction, and the diode D ₂ is turned on in the opposite direction. In this case, minority carriers through the drain node are removed from the space charge region of the semiconductor. With a complete depletion of the semiconductor by minority carriers, the second stable state of the device is realized, which allows it to be used as a capacitive key. The presence of two opposing pn junctions in the design ensures the absence of shunt conduction currents in all varicap operation modes.

Each of the equivalent capacitances C ₁ and C ₂ parallel to the diodes D ₁ and D _2, represents a sequential chain of capacities of individual diodes. This design provides a decrease in the own capacitance of the drainage node inversely to the number of regions of hole conductivity of the drainage node elements. As a result, the overlap in capacity increases.

The auxiliary dielectric 7 is structurally located in the localization region of the minority carrier drain node, provides isolation and eliminates the influence of surface leakage currents along the reverse surface of the semiconductor on the parameters of the device.

The design of the proposed MIS-varicap ensures the achievement of higher values of the main technical characteristics of the device: the limiting frequency and overlap in capacitance, will reduce the intrinsic capacitance of the drain node components of minority charge carriers and use it to control the frequency and phase of the alternating signal in the RF and microwave radio devices.

Claims (1)

A multi-element MIS varicap containing a semiconductor, a dielectric, a control electrode and a drain assembly of minority carriers with a pn region having a depth equal to the thickness of the semiconductor, characterized in that the drain assembly is made in the form of a set of alternating regions of electronic and hole conductivity, one of areas of the electronic type of conductivity of the drain node is connected to the control electrode, and the linear size of the elements of the drain node along the surface is equal to the linear size of the semiconductor.

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