WO1997045874A2 - Microwave monolithic integrated circuit with coplaner waveguide having silicon-on-insulator composite substrate - Google Patents
Microwave monolithic integrated circuit with coplaner waveguide having silicon-on-insulator composite substrate Download PDFInfo
- Publication number
- WO1997045874A2 WO1997045874A2 PCT/IB1997/000465 IB9700465W WO9745874A2 WO 1997045874 A2 WO1997045874 A2 WO 1997045874A2 IB 9700465 W IB9700465 W IB 9700465W WO 9745874 A2 WO9745874 A2 WO 9745874A2
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- silicon
- layer
- cpw
- ground planes
- conductivity
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P3/00—Waveguides; Transmission lines of the waveguide type
- H01P3/003—Coplanar lines
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/58—Structural electrical arrangements for semiconductor devices not otherwise provided for, e.g. in combination with batteries
- H01L23/64—Impedance arrangements
- H01L23/66—High-frequency adaptations
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/30—Technical effects
- H01L2924/301—Electrical effects
- H01L2924/3011—Impedance
Definitions
- Microwave monolithic integrated circuit with coplaner waveguide having silicon-on-insulator composite substrate having silicon-on-insulator composite substrate.
- the invention relates to the field of microwave monolithic integrated circuits (MMICs) for wireless applications, such as cellular radio and personal communication systems. More particularly, it relates to MMICs which include passive circuit elements and active amplifier stages which are coupled together by microwave transmission line in order to achieve reduced propagation loss of microwave signals conveyed there ⁇ between.
- MMICs microwave monolithic integrated circuits
- passive circuit elements such as resistors, inductors and capacitors are fabricated in monolithic form on a silicon substrate.
- Active amplifier stages are also fabricated in the monolithic structure, and are coupled to the passive elements by microwave transmission line.
- This has commonly taken the form of a microstrip line, which consists of a conducting strip on the upper surface of a silicon dioxide dielectric layer and a metal ground plane on the back surface.
- An MMIC structure of this kind is shown, for example, in Fig. 8-163 on page 105 of the text Electronics Engineers Handbook, McGraw Hill Book Co. , 3d ed. 1989.
- a major problem with such a structure is that the electric field component of a quasi-TEM electromagnetic wave must couple to the ground plane through the entire substrate, resulting in high propagation losses.
- This problem is avoided by providing a ground plane on the same surface of the silicon die as the conducting strip, resulting in a coplanar waveguide (CPW) structure.
- CPW coplanar waveguide
- This type of waveguide is also shown in the aforesaid Fig. 8-163 of the cited textbook.
- the small spatial separation between the conducting strip and the ground plane effectively confines the electric field to the near-surface of the substrate, reducing the depth of penetration into the body of the substrate.
- the transmission loss which is the inverse of the quality factor Q, is then dependent on the conductivity and consequently the doping level of the near-surface region of the substrate.
- the invention provides an MMIC which includes a coplanar waveguide
- CPW having a signal conductor and ground planes on the upper surface of a composite silicon structure consisting a monocrystalhne silicon substrate, a first insulating layer formed on the upper surface of the substrate, a relatively thin silicon layer formed on the surface of the first insulating layer, and a thinner second insulating layer formed as a dielectric on the surface of the thin silicon layer, the upper surface of the dielectric layer being the upper surface of the composite structure.
- the structure can be referred to as silicon-on-insulator, or SOI, the insulator being the first insulating layer.
- the region of the thin silicon layer underlying the signal conductor and extending between the ground planes is implanted with an active dopant, generally N-type, which is then thermally diffused so as to form a zone of high conductivity therein.
- an active dopant generally N-type
- the doping is perforfned so that the doped zone has a lateral gradient of decreasing concentration in a direction from the signal conductor to each of the ground planes.
- doping variations ranging from abrupt to linear can easily be obtained.
- the high conductivity of the diffused zone causes the elect ⁇ c field of a quasi-TEM wave to separate from the magnetic field and bend upward toward the upper dielectric layer, with minimal penetration of the underlying silicon substrate. This effect is enhanced even further when the diffused zone has a doping gradient as descnbed. A quality factor Q of approximately 15 has been attained, many times that achieved with a homogeneously doped silicon substrate body.
- the isolation of the electric wave from the substrate obviates the need for deep diffusion of the substrate, enabling choice of a substrate resistivity which minimizes radiation loss due to penetration by the magnetic component of the quasi-TEM wave.
- Active and passive circuit elements can be formed by conventional oxide masking and diffusion techniques in the silicon layer of the SIO structure, in regions thereof which are not used to form the CPW.
- Fig. 1 is a cross-sectional view of a prior art form of coplanar waveguide
- CPW CPW transmission line having a bulk silicon substrate, showing how the electric field lines of transmitted microwave deeply penetrate the substrate;
- Fig. 2 is a cross-sectional view of a coplanar waveguide having an SOI structure and a homogenously doped zone in the silicon layer of that structure
- Fig. 3 a cross-sectional view of a coplanar waveguide having a SOI structure and a lateral diffusion gradient in the doped zone in the silicon layer of that structure;
- Fig. 4 is a plan view of an MMIC in accordance with the invention, which includes a CPW as shown in Fig. 3 as well as various passive circuit elements and active amplifier stages; and
- Figs. 5-6 are successive steps of a method for fabricating the CPW shown in Fig. 3.
- CPW coplanar waveguide
- a metal conductor 1 a metal conductor 1 and a pair of metal ground planes 3a and 3b extending parallel thereto on either side thereof to provide ground return potential for the electric component of a quasi-TEM wave traversing along the length of the CPW.
- These elements are on the upper surface of a silicon substrate 5, which surface has been oxidized to form a thin layer 7 of Si ⁇ 2 which serves as a dielectric to insulate the ground planes from the conductor 1.
- the region of the upper surface of substrate 5 which laterally extends between the two ground planes is doped, by implantation and diffusion, with an active impurity (e.g., antimony, arsenic, phosphorous or boron), in order to form a zone 8 of high conductivity.
- an active impurity e.g., antimony, arsenic, phosphorous or boron
- Applicant has taken a different approach to the problem of reducing transmission loss in a CPW, by providing a structure as shown in Fig. 2.
- a zone 9 of the silicon layer extending between the ground planes 3a and 3b, is doped to obtain a high conductivity therein.
- the substrate may typically be 500 ⁇ thick, the oxide layer 11 40 ⁇ thick, and the silicon layer 9 only 10 ⁇ thick. It is therefore a simple matter to dope the layer 9 sufficiently to obtain high conductivity.
- the electric field lines, as shown in Fig. 2 by the dashed lines, are now largely confined within the layer 9 but there is nevertheless some degree of fringing into substrate 5. Accordingly, while the structure of Fig. 2 provides significantly lower transmission loss than that in Fig. 1 there is still room for improvement.
- Fig. 4 is a plan view of an MMIC in accordance with the invention, which incorporates two coplanar waveguides 13 and 15 of the kind shown in cross-section in Fig. 3.
- Both are formed in a monolithic integrated circuit chip 17 which also has formed therein a passive circuit element 19 such as a resistor, capacitor or inductor, an active amplifier stage 21 comprising a transistor, and a further passive circuit element 23.
- the actual connections between the CPWs and the circuit elements are conventional, and are omitted for clarity.
- the CPW 13 couples element 19 to the input of amplifier 21, and CPW 15 couples the output of amplifier 21 to the circuit element 23.
- the passive circuit elements and amplifier stage are all formed by conventional implantation and diffusion methods in the silicon layer 9 of an SOI structure comprising that layer and an underlying oxide layer 11 as shown in Fig. 3.
- the diffused zone formed in layer 9 in Fig. 3 is, of course, only provided where a CPW is to be formed.
- the CPW shown in Fig. 3 may be formed by a process as shown in Figs. 5-6.
- Fig. 5 shows in cross-section an SOI structure formed on a silicon substrate 5 of relatively high resistivity.
- the substrate may typically be 500 ⁇ thick, and the oxide layer 11 formed thereon may be 2 ⁇ thick.
- the actual thickness can, however, range from .02 ⁇ to lOOO ⁇ depending on the impedance which is desired for the particular application.
- the relatively thin monocrystalline silicon layer 9 is then formed on oxide layer 11. A method of achieving that is to bond layer 9 to the oxide layer by heating in an inert ambient atmosphere.
- the next step is to grow a thin oxide layer 7 on the surface of silicon layer 9, to serve as a pad oxide for controlled doping by implanting a selected impurity, typically N type, through a mask 15 having implantation windows therein for achieving a desired lateral concentration gradient. Any desired gradient can be achieved by size control of the implantation windows, a larger window size being allocated for higher concentration and the size being gradually decreased towards the lowest concentration.
- the resulting implanted regions are shown cross-hatched in Fig. 6.
- the structure is then heated to produce lateral diffusion, for example at a temperature of 1100° C for 24 hours.
- the ground planes and conducting line are then bonded to oxide layer 7, resulting in the final structure shown in Fig. 3.
- the diffusion mask and the thermal cycle can be selected so as to result, as noted above, in a doping variation ranging from abrupt to linear.
- upper surface has been used herein purely to identify one of two opposed surfaces of a relevant layer of the MMIC. Obviously, the entire structure can be used in any spatial orientation, so that the "upper surface” might in fact be facing downwardly.
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Semiconductor Integrated Circuits (AREA)
- Waveguides (AREA)
- Optical Integrated Circuits (AREA)
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP9541896A JPH11510671A (en) | 1996-05-30 | 1997-04-30 | Microwave monolithic integrated circuit with coplanar waveguide with SOI composite substrate |
EP97916616A EP0845157A2 (en) | 1996-05-30 | 1997-04-30 | Microwave monolithic integrated circuit with coplaner waveguide having silicon-on-insulator composite substrate |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/655,170 US5986331A (en) | 1996-05-30 | 1996-05-30 | Microwave monolithic integrated circuit with coplaner waveguide having silicon-on-insulator composite substrate |
US08/655,170 | 1996-05-30 |
Publications (2)
Publication Number | Publication Date |
---|---|
WO1997045874A2 true WO1997045874A2 (en) | 1997-12-04 |
WO1997045874A3 WO1997045874A3 (en) | 1998-02-12 |
Family
ID=24627805
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/IB1997/000465 WO1997045874A2 (en) | 1996-05-30 | 1997-04-30 | Microwave monolithic integrated circuit with coplaner waveguide having silicon-on-insulator composite substrate |
Country Status (4)
Country | Link |
---|---|
US (1) | US5986331A (en) |
EP (1) | EP0845157A2 (en) |
JP (1) | JPH11510671A (en) |
WO (1) | WO1997045874A2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1999034443A1 (en) * | 1997-12-15 | 1999-07-08 | Stratedge Corporation | Ceramic microelectronics package with co-planar waveguide feed-through |
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EP0845157A2 (en) | 1998-06-03 |
US5986331A (en) | 1999-11-16 |
JPH11510671A (en) | 1999-09-14 |
WO1997045874A3 (en) | 1998-02-12 |
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