JP2006253503A - Microwave monolithic integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To assure a broad capacitance-variation-width of a varactor diode with a high withstand voltage property and an excellent high speed property of an HBT maintained. <P>SOLUTION: In a microwave monolithic integrated circuit with the HBT 20 and the varactor diode 21 formed on a common semi-insulating substrate 1, a collector layer common to the HBT and the varactor diode 21 comprises first collector layers 22a, 22b positioning at the side of a collector contact layer 4 and second collector layers 23a, 23b positioning at the side of an anti-collector layer. Further, carrier densities of the first collector layers are set higher than that of the second collector layers. And a Schottky electrode 24 is formed on the second collector layer 23b in the varactor diode 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microwave monolithic integrated circuit in which a heterostructure bipolar transistor and a varactor diode are formed on one common semi-insulating substrate.

  For example, in order to realize an oscillator (voltage controlled oscillator) whose oscillation frequency is a high frequency such as 10 GHz to 100 GHz and whose oscillation frequency can be varied in a wide range, a transistor with excellent high-speed operation and an applied voltage are used. It is necessary to develop a varactor diode whose capacitance between electrodes changes greatly.

  Heterojunction Bipolar Transistor (HBT, hereinafter abbreviated as HBT) is used as the transistor, and the microwave monolithic integration in which the heterostructure bipolar transistor and the varactor diode are formed on one common semi-insulating substrate. Non-Patent Document 1 reports a voltage controlled oscillator (VCO) using a circuit (Microwave Monolithic Integrated Circuit; MMIC).

  In this microwave monolithic integrated circuit, a pn junction (pn diode) formed by a base layer and a collector layer corresponding to a base-collector junction in a heterostructure bipolar transistor formed on a common semi-insulating substrate is a varactor. Used as a diode.

  FIG. 6 shows a cross-sectional view of a microwave monolithic integrated circuit in which a heterostructure bipolar transistor (HBT) and a varactor diode using a pn junction are formed on a common semi-insulating substrate. As shown in the figure, an HBT 2 is formed on one side of one common semi-insulating GaAs substrate 1 and a varactor diode 3 is formed on the other side.

In the HBT 2, a collector contact layer 4 having a thickness of 400 nm made of GaAs containing n-type impurities at a high concentration (5 × 10 ¹⁸ cm ⁻³ ) is formed on a semi-insulating GaAs substrate 1. A collector layer 5a having a thickness of 300 nm made of GaAs containing an n-type impurity having a concentration of 5 × 10 ¹⁵ cm ⁻³ is formed on the upper side of the collector layer, and a high concentration (6 × 10 ¹⁹ cm ⁻³ ) is formed on the collector layer 5a. A base layer 6a having a thickness of 35 nm made of GaAs containing p-type impurities is formed, and an emitter layer 7 having a thickness of 60 nm made of GaAs containing n-type impurities at a concentration of 5 × 10 ¹⁷ cm ⁻³ is formed above the base layer 6a. Is formed.

A carrier concentration relaxation layer 8 having a thickness of 100 nm and made of GaAs containing an n-type impurity having a concentration of 5 × 10 ¹⁸ cm ⁻³ is formed on the upper side of the emitter layer 7. A 50 nm thick composition relaxation layer 9 made of InGaAs containing an n-type impurity having a concentration of 10 ¹⁹ cm ⁻³ is formed, and a high resistance for making ohmic contact with the emitter layer 7 is formed above the composition relaxation layer 9. An emitter contact layer 10 having a thickness of 50 nm and made of InGaAs containing n-type impurities at a concentration (5 × 10 ¹⁹ cm ⁻³ ) is formed.

  The emitter layer 7, the carrier concentration relaxation layer 8, the composition relaxation layer 9, and the emitter contact layer 10 located above the base layer 6a are formed in a mesa shape.

  An emitter electrode 11 is formed on the upper surface of the emitter contact layer 10, a collector electrode 12 is attached in the vicinity of both ends of the upper surface of the collector contact layer 4, and a base electrode 13 is attached in the vicinity of both ends of the upper surface of the base layer 6a.

  In the varactor diode 3, a collector contact layer 4 common to the HBT 2 is formed on the semi-insulating GaAs substrate 1, and a collector layer 5b which is the same layer as the collector layer 5a of the HBT 2 is formed above the collector contact layer 4. Is formed. A base layer 6b that is the same layer as the base layer 6a of the HBT 2 is formed above the collector layer 5b. A cathode electrode 14 is attached in the vicinity of both ends on the upper surface of the collector contact layer 4, and an anode electrode 15 is attached on the upper surface of the base layer 6b.

  Further, on both side portions of the HBT 2 and both side portions of the varactor diode 3, high resistance regions 16 are formed which are made high resistance by ion implantation in order to electrically isolate the elements of the HBT 2 and the varactor diode 3 from each other.

In the microwave monolithic integrated circuit configured as described above, the varactor diode 3 has a base layer 6a made of p-type GaAs having a high concentration (6 × 10 ¹⁹ cm ⁻³ ) and a low concentration (5 × 10 ¹⁵ cm ^{−). The} collector layer 5a made of n-type GaAs of ³ ) forms a pn diode.
Yoshiki Yamauchi, et al., “A 15GHz Monolithic Low-Phase-Noise VCO Using AlGaAs / GaAs HBT Technology,” IEEE Journal of Solid State Circuits, Vol.27, pp.1444-1447,1992

  However, the microwave monolithic integrated circuit shown in FIG. 6 still has the following problems to be solved.

  That is, in the varactor diode 3, since the thickness (depletion layer amount) of the depletion layer in the n-type collector layer 5b at the pn junction changes according to the applied voltage applied between the electrodes, the cathode electrode corresponds to the applied voltage. The capacitance between 14 and the anode electrode 15 changes.

  In this case, the voltage dependency of the capacitance increases as the thickness of the depletion layer in the collector layer 5b when the applied voltage is zero. The thickness of the depletion layer in the collector layer 5b when the applied voltage is zero is determined by the thickness of the collector layer 5b, the carrier concentration, and the like.

  Therefore, in order to increase the variable capacitance width of the varactor diode 3, it is conceivable to reduce the thickness of the collector layer 5b, reduce the carrier concentration of the collector layer 5b, or the like.

  In the microwave monolithic integrated circuit, the base layer 6a of the HBT 2 and the base layer 6b of the varactor diode 3 are the same layer, and the collector layer 5a of the HBT 2 and the collector layer 5b of the varactor diode 3 are the same layer.

Therefore, when the thickness of the collector layer 5b of the varactor diode 3 is reduced, the withstand voltage characteristic between the base and the collector in the HBT 2 described above is lowered. Therefore, the voltage characteristics of the HBT 2 are deteriorated. Also, reducing the carrier concentration of the collector layer 5b, the base-collector junction capacitance C _BC is increased, high-speed performance (frequency characteristics) of HBT2 decreases.

  As described above, in the microwave monolithic integrated circuit in which the conventional HBT 2 and the varactor diode 3 using the pn diode are formed, the high withstand voltage characteristic and the excellent high-speed characteristic in the HBT 2 are maintained. A wide capacity variable width could not be secured. The small capacitance variable width means that the adjustment width (tuning width) of the oscillation frequency of the oscillator in which the microwave monolithic integrated circuit is incorporated is small.

  The present invention has been made in view of such circumstances, and provides a microwave monolithic integrated circuit capable of ensuring a wide capacitance variable width in a varactor diode while maintaining high withstand voltage characteristics and excellent high-speed characteristics in an HBT. The purpose is to do.

The present invention relates to a microwave monolithic integrated circuit in which a heterostructure bipolar transistor in which a collector contact layer, a collector layer, a base layer, and an emitter layer are stacked on one common semi-insulating substrate and a varactor diode are formed.
The varactor diode has a collector contact layer that is the same as the collector contact layer of the heterostructure bipolar transistor and a collector layer that is the same layer as the collector layer of the heterostructure bipolar transistor. Further, in the varactor diode, a cathode electrode that is ohmic-connected is formed on the same collector contact layer, and an anode electrode that is Schottky-connected is formed on the same collector layer.

  In the microwave monolithic integrated circuit configured as described above, the varactor diode forms a Schottky diode, for example, by a collector layer that is an n-type semiconductor and an anode electrode that is a metal. Also in such a Schottky diode, a depletion layer is formed in the vicinity of an anode electrode (Schottky electrode) that is a metal in a collector layer that is an n-type semiconductor in contact with the Schottky electrode. The size of the depletion layer formed in the vicinity of the anode electrode is smaller than when the collector layer is in contact with the base layer that is a p-type semiconductor.

  As a result, when the voltage applied between the cathode electrode and the anode electrode is changed, the size of the depletion layer is greatly changed, and the voltage dependency of the capacitance between the cathode electrode and the anode electrode is increased. A variable width can be secured.

  In addition, since the thickness and carrier concentration of the collector layer itself are not changed, the withstand voltage characteristic and the high speed characteristic in the HBT do not change.

  In another invention, the carrier concentration in the collector layer of the same layer common to the HBT and the varactor diode is set high on the collector contact layer side and low on the anti-collector contact layer side in the microwave monolithic integrated circuit of the invention described above. is doing.

  Another invention is the microwave monolithic integrated circuit of the above-described invention, wherein the same collector layer common to the HBT and the varactor diode is provided with a first collector layer located on the collector contact layer side and an anti-collector contact layer. And the second collector layer positioned on the side, and the carrier concentration of the first collector layer is set higher than the carrier concentration of the second collector layer.

  In the microwave monolithic integrated circuit configured as described above, the thickness of the entire collector layer in contact with the Schottky electrode in the varactor diode is not changed, and the carrier concentration changes in the thickness direction of the collector layer. Therefore, when the applied voltage is zero, the thickness (depletion layer amount) of the depletion layer formed on the Schottky electrode (anode electrode) side can be reduced. That is, when the applied voltage is low, the capacitance between the electrodes is extremely small, and when the applied voltage increases, the depletion layer thickness reaches the collector contact layer side where the carrier concentration is high, so the capacitance between the electrodes increases rapidly. To do. Therefore, the voltage dependency of the capacitance between the cathode electrode and the anode electrode is further increased, and a wider variable capacitance width in the varactor diode can be ensured.

On the other hand, also in the HBT, the carrier concentration changes in the thickness direction of the collector layer without changing the thickness of the entire collector layer existing between the base layer and the collector contact layer. In this way, by reducing the carrier concentration on the base layer side of the collector layer and increasing the carrier concentration on the collector contact layer side, the thickness of the depletion layer generated on the base layer side of the collector layer is uniform in all thickness directions. Since it is thinner than a conventional collector layer having a concentration, the collector travel time τ _C required for traveling in the collector layer of electrons is shortened, and as a result, the operation speed as a transistor is increased.

  In addition, since the thickness of the whole collector layer does not change, a withstand voltage property does not fall.

In the HBT, a region located outside the region facing the emitter layer in the first collector layer is depleted because the activation rate of the n-type impurity is reduced by ion implantation, and the base-collector junction capacitance C _BC can be reduced as needed.

  As described above, a wide capacitance variable width in the varactor diode can be ensured while maintaining high withstand voltage characteristics and excellent high-speed characteristics in the HBT.

  Another invention is the depletion layer formed in the vicinity of the anode electrode in the collector layer in the microwave monolithic integrated circuit of the invention described above in a state where no voltage is applied between the anode electrode and the cathode electrode of the varactor diode. The thickness of the collector layer in contact with the anode electrode is set to be thinner by etching than the thickness of the collector layer in contact with the base layer of the heterostructure bipolar transistor so that the thickness of the transistor is 200 nm or less.

  As described above, it was experimentally confirmed that when the thickness of the depletion layer is 200 nm or less, a wide variable capacitance width in the varactor diode can be secured in a state where the high withstand voltage characteristic and the excellent high speed characteristic in the HBT are maintained.

  Another invention is the microwave monolithic integrated circuit according to the invention described above, wherein the collector layer of the heterostructure bipolar transistor is a first collector layer located on the collector contact layer side and a first collector layer located on the anti-collector contact layer side. 2 collector layers. Further, the first collector layer and the second collector layer are formed of different types of semiconductor materials, and the band gap energy of the first collector layer is made larger than the band gap energy of the second collector layer. Yes.

  On the other hand, the collector layer of the varactor diode is composed of only the first collector layer which is the same layer as the first collector layer of the heterostructure bipolar transistor, and the anode electrode is formed on the first collector layer.

  For example, in a microwave monolithic integrated circuit employing an InP substrate as a semi-insulating substrate, the collector layer in contact with the base layer of the heterostructure bipolar transistor is formed of a semiconductor material having a relatively small band gap energy. When a varactor diode is formed in this state, a collector layer of a semiconductor material having a relatively small band gap energy is in direct contact with the Schottky electrode (anode electrode). It is preferable to bring a semiconductor material having a large band gap energy into contact with the Schottky electrode.

  Therefore, the collector layer of the heterostructure bipolar transistor is composed of two types of semiconductor materials having different band gap energies, and the Schottky electrode of the varactor diode (on the upper surface of the first collector layer, which is the semiconductor material having the larger band gap energy). Anode electrode).

  In a microwave monolithic integrated circuit in which an HBT and a varactor diode are formed on a common semi-insulating substrate, the varactor diode is connected to a collector contact layer, a collector layer, an ohmic-connected cathode electrode, and a Schottky-connected anode. It consists of electrodes.

  Accordingly, it is possible to secure a wide capacitance variable width in the varactor diode while maintaining the withstand voltage characteristics and the excellent high speed characteristics.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing a schematic configuration of a microwave monolithic integrated circuit according to the first embodiment of the present invention. The same parts as those of the conventional microwave monolithic integrated circuit shown in FIG.

  In the microwave monolithic integrated circuit of the first embodiment, an HBT 20 is formed on one side on one common semi-insulating GaAs substrate 1 and a varactor diode 21 is formed on the other side.

In the HBT 20, a collector contact layer 4 having a thickness of 400 nm made of GaAs containing n-type impurities at a high concentration (5 × 10 ¹⁸ cm ⁻³ ) is formed on a semi-insulating GaAs substrate 1. A first collector layer 22a having a thickness of 300 nm made of GaAs containing an n-type impurity having a concentration of 1.5 × 10 ¹⁷ cm ⁻³ is formed on the upper side of the first collector layer 22a. A second collector layer 23a having a thickness of 200 nm made of GaAs containing an n-type impurity having a concentration of 10 ¹⁶ cm ⁻³ is formed.

A base layer 6a having a thickness of 35 nm made of GaAs containing p-type impurities at a high concentration (6 × 10 ¹⁹ cm ⁻³ ) is formed on the upper side of the second collector layer 23a, and 5 × on the upper side of the base layer 6a. An emitter layer 7 having a thickness of 60 nm made of GaAs containing an n-type impurity having a concentration of 10 ¹⁷ cm ⁻³ is formed.

A carrier concentration relaxation layer 8 having a thickness of 100 nm and made of GaAs containing an n-type impurity having a concentration of 5 × 10 ¹⁸ cm ⁻³ is formed on the upper side of the emitter layer 7. A 50 nm thick composition relaxation layer 9 made of InGaAs containing an n-type impurity with a concentration of 10 ¹⁹ cm ⁻³ is formed, and a high resistance for obtaining ohmic contact with the emitter layer 7 is formed above the composition relaxation layer 9. An emitter contact layer 10 having a thickness of 50 nm and made of InGaAs containing n-type impurities at a concentration (5 × 10 ¹⁹ cm ⁻³ ) is formed.

  An emitter electrode 11 is formed on the upper surface of the emitter contact layer 10, a collector electrode 12 is attached in the vicinity of both ends of the upper surface of the collector contact layer 4, and a base electrode 13 is attached in the vicinity of both ends of the upper surface of the base layer 6a.

Further, in this HBT 20, the portion not facing the emitter layer 7 of the second collector layer 23a and the first collector layer 22a is, by ion implantation to reduce the base-collector junction capacitance C _BC, High depleted A high resistance region 25 having resistance is formed.

In the varactor diode 21, a collector contact layer 4 common to the HBT 20 is formed on the semi-insulating GaAs substrate 1, and the same layer as the first collector layer 22 a of the HBT 20 is formed above the collector contact layer 4. A first collector layer 22b having a thickness of 300 nm and made of GaAs containing an n-type impurity having a concentration of .5 × 10 ¹⁷ cm ⁻³ is formed. On the upper side of the first collector layer 22b, a second collector layer 23b having a thickness of 100 nm and made of GaAs containing an n-type impurity having a concentration of 2.5 × 10 ¹⁶ cm ⁻³ is formed.

  Specifically, after forming a 400 nm collector contact layer, a 300 nm first collector layer, and a 200 nm second collector layer to be used with the HBT 20 and the varactor diode 21 on the semi-insulating GaAs substrate 1, this 200 nm is formed. A portion corresponding to the varactor diode 21 in the second collector layer is etched by 100 nm from above to obtain a second collector layer 23b having a thickness of 100 nm.

  A cathode electrode 14 that is ohmic-connected is provided near both ends of the upper surface of the collector contact layer 4, and an anode electrode (Schottky electrode) 24 that is Schottky-connected is mounted on the upper surface of the second collector layer 23b.

  Therefore, in the varactor diode 21, a metal anode electrode (Schottky electrode) 24, the second collector layer 23b, and the first collector layer 23b form a Schottky diode.

  The amount of etching of the 200 nm second collector layer from above is such that the second collector layer 23b, the first collector layer 23b, and the first collector layer are in a state where no voltage is applied between the anode electrode (Schottky electrode) 24 and the cathode electrode 14. The thickness of the depletion layer formed in the vicinity of the anode electrode (Schottky electrode) 24 in the collector layer 22b is 200 nm or less.

  Further, on both side portions of the HBT 20 and both side portions of the varactor diode 21, high resistance regions 16 are formed which are made high resistance by ion implantation in order to electrically isolate the elements of the HBT 20 and the varactor diode 21 from each other.

  The characteristics of the microwave monolithic integrated circuit of the first embodiment configured as described above will be described.

  As described above, the varactor diode 21 is configured by a Schottky diode including the second collector layer 23b that is an n-type semiconductor and an anode electrode (Schottky electrode) 24 that is a metal. The size of the depletion layer formed in the vicinity of the anode electrode (Schottky electrode) 24 in the second collector layer 23 b in contact with the anode electrode (Schottky electrode) 24 is the base layer in which this collector layer is a p-type semiconductor. Small compared to when touching.

  Further, the collector layer in contact with the anode electrode (Schottky electrode) 24 in the varactor diode 21 is divided into first and second collector layers 22b and 23b, and the second collector layer in contact with the anode electrode (Schottky electrode) 24 is divided. The carrier concentration of 23b is lowered. Therefore, when the applied voltage is zero, the thickness of the depletion layer formed on the anode electrode (Schottky electrode) 24 side can be reduced. Therefore, as described above, the voltage dependency of the capacitance between the cathode electrode 14 and the anode electrode 24 is further increased, and a wider capacitance variable width in the varactor diode 21 can be secured.

  In this case, it has been proved experimentally that the thickness of the depletion layer formed on the anode electrode (Schottky electrode) 24 side when the applied voltage is zero is 200 nm or less. The thickness of the depletion layer is affected by the thickness of the second collector layer 23b and the carrier concentration ratio of the first and second collector layers 22b and 23b, so that the thickness of the depletion layer is 200 nm or less. The thickness of the second collector layer 23b on the varactor diode 21 side is set.

  Further, since the carrier concentration of the second collector layer 23b in contact with the anode electrode (Schottky electrode) 24 is low, the reverse leakage current is suppressed to a low level, and the withstand voltage characteristic of the varactor diode 21 itself can be ensured.

On the other hand, in the HBT 20 as well, the entire thickness of the first and second collector layers 22a and 23a existing between the base layer 6a and the collector contact layer 4 is not changed, and the second collector layer on the base layer 6a side is not changed. The carrier concentration of 23a is set low, and the carrier concentration of the twelfth collector layer 22a on the collector contact layer 2 side is set high. Therefore, since the thickness of the depletion layer generated on the base layer 6a side of the second collector layer 23a is reduced, the collector travel time τ _C required for traveling in the collector layer of electrons is shortened, and as a result, the transistor as a transistor is reduced. Increases operating speed.

  In addition, since the thickness of the whole collector layer does not change, a withstand voltage property does not fall.

Further, as described above, in this HBT 20, the portions of the second collector layer 23a and the first collector layer 22a that do not face the emitter layer 7 are depleted and increased in resistance by ion implantation. 25 is formed. As a result, the base-collector junction capacitance C _BC is reduced.

  In this manner, a wide capacitance variable width in the varactor diode 21 can be ensured while maintaining high withstand voltage characteristics and excellent high-speed characteristics in the HBT 20.

  FIG. 4 is a diagram showing an experimental result of applied voltage dependence of interelectrode capacitance in a varactor diode. As can be understood from the experimental results, the voltage dependency of the capacitance of the varactor diode 21 of the first embodiment is much larger than the voltage dependency of the capacitance of the conventional varactor diode 3 using a pn diode.

FIG. 5 is a diagram illustrating experimental results of the relationship between the collector current, the current gain cutoff frequency f _T , and the maximum oscillation frequency fmax in the HBT 20 of the first embodiment. As can be understood from the experimental results, the HBT 20 of the first embodiment maintains sufficiently high speed characteristics (frequency characteristics).

(Second Embodiment)
FIG. 2 is a sectional view showing a schematic configuration of a microwave monolithic integrated circuit according to the second embodiment of the present invention. The same parts as those of the conventional microwave monolithic integrated circuit shown in FIG.

  In the microwave monolithic integrated circuit of the second embodiment, an HBT 26 is formed on one side of a common semi-insulating GaAs substrate 1 and a varactor diode 27 is formed on the other side.

In the HBT 26 according to the second embodiment, the portion of the collector layer 5a made of GaAs containing n-type impurities having a concentration of 5 × 10 ¹⁵ cm ⁻³ having a thickness of 300 nm that does not face the emitter layer 7 is a base-collector junction capacitance C. _In order to reduce _BC , a high resistance region 25 which is depleted and has a high resistance is formed by ion implantation. The other configuration is the same as that of the HBT 2 of the conventional monolithic integrated circuit of FIG.

On the other hand, in the varactor diode 27, the collector contact layer 4 common to the HBT 26 is formed on the semi-insulating GaAs substrate 1, and 5 × which is the same layer as the contact layer 5a of the HBT 26 is formed above the collector contact layer 4. A collector layer 5c having a thickness of 200 nm made of GaAs containing an n-type impurity having a concentration of 10 ¹⁵ cm ⁻³ is formed.

  Specifically, a 400 nm collector contact layer and a 300 nm collector layer used together with the HBT 26 and the varactor diode 27 are formed on the semi-insulating GaAs substrate 1, and then a portion corresponding to the varactor diode 27 in the 300 nm collector layer. Is etched by 100 nm from above to obtain a collector layer 5b having a thickness of 200 nm.

  Cathode electrodes 14 that are ohmic-connected are provided near both ends of the upper surface of the collector contact layer 4, and an anode electrode (Schottky electrode) 24 that is Schottky-connected is mounted on the upper surface of the collector layer 5c.

  Therefore, in the varactor diode 27, the anode electrode (Schottky electrode) 24 made of metal and the collector layer 5c form a Schottky diode.

  Note that the amount of etching of the 300 nm collector layer from above is such that the anode electrode (Schottky electrode) 24 in the collector layer 5 c is in a state where no voltage is applied between the anode electrode (Schottky electrode) 24 and the cathode electrode 14. This is the value at which the thickness of the depletion layer formed in the vicinity is 200 nm or less.

  In the microwave monolithic integrated circuit of the second embodiment configured as described above, the varactor diode 27 is an n-type semiconductor collector, similar to the varactor diode 21 of the monolithic integrated circuit of the first embodiment shown in FIG. It is composed of a Schottky diode having a layer 5c and a metal anode electrode (Schottky electrode) 24. The depletion layer formed in the vicinity of the anode electrode (Schottky electrode) 24 in the collector layer 5 c in contact with the anode electrode (Schottky electrode) 24 is in contact with the base layer that is a p-type semiconductor. Small compared to the case. Furthermore, the thickness of the depletion layer in a state where no voltage is applied between the electrodes is set to 200 nm or less. Therefore, the voltage dependency of the capacitance between the cathode electrode 14 and the anode electrode 24 is increased, and a wide capacitance variable width in the varactor diode 27 can be secured.

On the other hand, in the HBT 26, since the thickness and carrier concentration of the collector layer 5a itself are not changed, the withstand voltage characteristics in the HBT 26 are not changed. Further, a high resistance region 25 is formed in a portion of the collector layer 5a that does not face the emitter layer 7. Accordingly, the base-collector junction capacitance _CBC is reduced, and the high-speed characteristics are improved.

  Therefore, also in the microwave monolithic integrated circuit of the second embodiment, as in the microwave monolithic integrated circuit of the first embodiment described above, the varactor is maintained while maintaining the high withstand voltage characteristics and the excellent high-speed characteristics in the HBT 26. A wide capacitance variable width in the diode 27 can be secured.

  FIG. 4 shows the experimental results of the relationship between the applied voltage and the capacitance between the electrodes in the varactor diode 27 of the second embodiment. As can be understood from the experimental results, the voltage dependence of the capacitance of the varactor diode 27 of the second embodiment is larger than the voltage dependence of the capacitance of the conventional varactor diode 3 using a pn diode.

(Third embodiment)
FIG. 3 is a cross-sectional view showing a schematic configuration of a microwave monolithic integrated circuit according to the third embodiment of the present invention. The same parts as those of the microwave monolithic integrated circuit of the first embodiment shown in FIG.

  In the microwave monolithic integrated circuit according to the third embodiment, an HBT 28 is formed on one side on one common semi-insulating InP substrate 31, and a varactor diode 29 is formed on the other side.

In the HBT 28, a collector contact layer 32 made of InP containing a high concentration (2 × 10 ¹⁹ cm ⁻³ ) of n-type impurities is formed on a semi-insulating InP substrate 31, and this collector contact layer 32 is formed. A first collector layer 33a having a thickness of 200 nm and made of InP containing an n-type impurity having a concentration of 1.5 × 10 ¹⁷ cm ⁻³ is formed on the upper side of the first collector layer 33a. An n-type impurity is placed on the upper side of the first collector layer 33a. A composition graded layer 34 made of InGaAlAs and having a thickness of 30 nm is formed, and a second collector layer 35 made of undoped InGaAs and having a thickness of 150 nm is formed on the composition graded layer 34.

On the upper side of the second collector layer 35 is formed a base layer 36 made of InGaAs containing a high concentration (4 × 10 ¹⁹ cm ⁻³ ) of p-type impurities, and above this base layer 36 3 × An emitter layer 37 having a thickness of 50 nm and made of InP containing an n-type impurity having a concentration of 10 ¹⁷ cm ⁻³ is formed.

A 20 nm thick carrier concentration relaxation layer 38 made of InP containing an n-type impurity having a concentration of 2 × 10 ¹⁹ cm ⁻³ is formed on the emitter layer 37, and the emitter layer is formed above the carrier concentration relaxation layer 38. An emitter contact layer 39 having a thickness of 70 nm and made of InGaAs containing an n-type impurity at a high concentration (3 × 10 ¹⁹ cm ⁻³ ) for achieving ohmic contact with the substrate 37 is formed.

  The emitter electrode 11 is formed on the upper surface of the emitter contact layer 39, the collector electrode 12 is attached in the vicinity of both ends of the upper surface of the collector contact layer 32, and the base electrode 13 is attached in the vicinity of both ends of the upper surface of the base layer 36.

In the varactor diode 29, a collector contact layer 32 common to the HBT 28 is formed on the semi-insulating InP substrate 31, and the first collector layer 33a of the HBT 28 is the same layer as the first collector layer 33a above the collector contact layer 32. A first collector layer 33b having a thickness of 180 nm and made of InP containing an n-type impurity having a concentration of 5 × 10 ¹⁷ cm ⁻³ is formed.

  Specifically, a 400 nm collector contact layer and a 200 nm first collector layer used together with the HBT 28 and the varactor diode 29 are formed on the semi-insulating InP substrate 31, and then the varactor in the 200 nm first collector layer is formed. A portion corresponding to the diode 29 is etched by 20 nm from above to obtain a first collector layer 33b having a thickness of 180 nm.

  A cathode electrode 14 that is ohmic-connected is provided near both ends of the upper surface of the collector contact layer 32, and an anode electrode (Schottky electrode) 24 that is Schottky-connected is attached to the upper surface of the first collector layer 33b.

  Accordingly, in the varactor diode 29, the anode electrode (Schottky electrode) 24 made of metal and the first collector layer 33b form a Schottky diode.

  In the microwave monolithic integrated circuit of the third embodiment configured as described above, in the varactor diode 29, the thickness of the depletion layer formed on the anode electrode (Schottky electrode) 24 side when the applied voltage is zero is The carrier concentration and thickness of the first collector layer 33b in contact with the anode electrode (Schottky electrode) 24 are set so as to be 200 nm or less. Therefore, it is possible to ensure a wide capacitance variable width in the varactor diode 29 while maintaining high withstand voltage characteristics and excellent high-speed characteristics in the HBT 28.

Further, the semiconductor material of the first collector layer 33 b in contact with the anode electrode (Schottky electrode) 24 is an n-type impurity having a concentration of 1.5 × 10 ¹⁷ cm ⁻³ which is the same layer as the first collector layer 33 a of the HBT 28. It is InP containing. The band gap energy of InP is larger than the band gap energy of InPGaAs which is a semiconductor material of the second collector layer 35 in contact with the base layer 36 of the HBT 28. Therefore, since the reverse leakage current in the varactor diode 29 is suppressed to a low level, sufficient withstand voltage characteristics can be ensured.

Sectional drawing which shows schematic structure of the microwave monolithic integrated circuit concerning 1st Embodiment of this invention Sectional drawing which shows schematic structure of the microwave monolithic integrated circuit concerning 2nd Embodiment of this invention. Sectional drawing which shows schematic structure of the microwave monolithic integrated circuit concerning 3rd Embodiment of this invention. The figure which shows the voltage dependence characteristic of the capacity | capacitance in the varactor diode integrated in the microwave monolithic integrated circuit of each embodiment of this invention. The figure which shows the frequency characteristic in HBT integrated in the microwave monolithic integrated circuit of 1st Embodiment of this invention. Sectional drawing which shows schematic structure of the conventional microwave monolithic integrated circuit

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semi-insulating GaAs substrate, 2, 20, 26, 28 ... HBT, 3, 21, 27, 29 ... Varactor diode, 4, 32 ... Collector contact layer, 5a, 5b, 5c ... Collector layer, 6a, 6b, 36 ... Base layer, 7, 37 ... Emitter layer, 8, 38 ... Carrier concentration relaxation layer, 9 ... Composition relaxation layer, 10, 39 ... Emitter contact layer, 11 ... Emitter electrode, 12 ... Collector electrode, 13 ... Base electrode, 14 ... cathode electrode, 15, 24 ... anode electrode (Schottky electrode), 16, 25 ... high resistance region, 22a, 22b, 33a, 33b ... first collector layer, 23a, 23b ... second collector layer, 31 ... Semi-insulating InP substrate

Claims (5)

In a microwave monolithic integrated circuit in which a heterostructure bipolar transistor in which a collector contact layer, a collector layer, a base layer, and an emitter layer are stacked on one common semi-insulating substrate, and a varactor diode are formed.
The varactor diode is
A collector contact layer that is the same layer as the collector contact layer of the heterostructure bipolar transistor, and a collector layer that is the same layer as the collector layer of the heterostructure bipolar transistor;
A microwave monolithic integrated circuit, wherein a cathode electrode that is ohmically connected is formed on the collector contact layer of the same layer, and an anode electrode that is Schottky connected is formed on the collector layer of the same layer.   2. The microwave monolithic integration according to claim 1, wherein a carrier concentration in the collector layer of the same layer common to the heterostructure bipolar transistor and the varactor diode is high on the collector contact layer side and low on the anti-collector contact layer side. circuit. The same collector layer common to the heterostructure bipolar transistor and the varactor diode is composed of a first collector layer located on the collector contact layer side and a second collector layer located on the anti-collector contact layer side. ,
2. The microwave monolithic integrated circuit according to claim 1, wherein the carrier concentration of the first collector layer is higher than the carrier concentration of the second collector layer.   The collector layer in contact with the anode electrode so that a thickness of a depletion layer formed in the vicinity of the anode electrode in the collector layer is 200 nm or less in a state where no voltage is applied between the anode electrode and the cathode electrode. 2. The microwave monolithic integrated circuit according to claim 1, wherein the thickness is set to be thinner by etching than the thickness of the collector layer in contact with the base layer of the heterostructure bipolar transistor. The collector layer of the heterostructure bipolar transistor includes a first collector layer located on the collector contact layer side and a second collector layer located on the anti-collector contact layer side, and the first collector layer and the The second collector layer is formed of a different semiconductor material, and the band gap energy of the first collector layer is larger than the band gap energy of the second collector layer,
The collector layer of the varactor diode is composed of a first collector layer that is the same layer as the first collector layer of the heterostructure bipolar transistor, and the anode electrode is formed on the first collector layer. The microwave monolithic integrated circuit according to claim 4.

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