Radio frequency monolithic integrated circuit and method for manufacturing the same
View Patent ↗The purpose of this invention is to realize a radio frequency monolithic integrated circuit high in performance, small in size and low in cost, where transistors and passive elements are arranged on a chip in which a conductive silicon substrate functions as a ground. Since the electromagnetic fields of passive elements induce a current in a conductive silicon substrate, a loss due to generation of Joule heat or the like occurs to lead to deterioration of the performance of the passive elements. To solve this problem, an SOI layer comprising a semiconductor layer having a large thickness and a high resistivity and a conductive silicon substrate is used, and passive elements and an active element are formed on the same substrate. Alternatively, a cavity is provided in the conductive substrate directly beneath the SOI layer in the region where the passive elements are formed, thereby attaining the object.
1. A radio frequency monolithic integrated circuit comprising:
a conductive substrate having a first resistivity;
a first insulation film formed on a face of said conductive substrate;
a semiconductor substrate provided on said first insulation film and having a second resistivity higher than said first resistivity;
a second insulation film provided on said semiconductor substrate;
an active element formed in one region of said semiconductor substrate;
a passive element provided on said second insulation film; and
a conductive region which penetrates through said semiconductor substrate, said first insulation film and said second insulation film and which connects a predetermined terminal of said active element and said conductive substrate to each other.
2. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein the thickness of said semiconductor substrate is greater than the thickness of said second insulation film or the thickness of a metal film formed on said second insulation film.
3. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein the thickness of said semiconductor substrate is greater than the sum of the thicknesses of said second insulation film and said metal film.
4. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein said second resistivity is not less than 100 Ω·cm.
5. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein a recessed portion as a cavity is provided in a region directly beneath said passive element, in said conductive substrate.
6. A radio frequency monolithic integrated circuit as set forth in claim 5 , wherein an insulating material is buried in said recessed portion.
7. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein said conductive region in said semiconductor substrate is composed of a plurality of adjacent regions, and a region having a resistivity lower than that of the other regions of said semiconductor substrate is present between said adjacent conductive regions.
8. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein said passive element comprises a microstrip line in which a metal film on said second insulation film is used as an upper electrode, and said semiconductor substrate is used as a lower electrode.
9. A radio frequency monolithic integrated circuit as set forth in claim 1 , wherein said active element is a power amplifying transistor, and said passive element is an impedance matching inductor or capacitance or a microstrip line.
10. A radio frequency monolithic integrated circuit as set forth in claim 9 , wherein said power amplifying transistor is a bipolar transistor.
11. A radio frequency monolithic integrated circuit as set forth in claim 10 , wherein a base layer of said bipolar transistor is made of a silicon-germanium alloy.
12. A method for manufacturing a radio frequency monolithic integrated circuit, comprising the steps of:
bonding a conductive substrate having a first resistivity and a semiconductor substrate having a second resistivity higher than said first resistivity to each other, with a first insulation film provided on said semiconductor substrate therebetween, and thinning said semiconductor substrate to a film with a predetermined thickness;
forming a second insulation film on said semiconductor substrate;
forming an active element in one region of said semiconductor substrate, and forming a passive element on said second insulation film; and
forming a conductive region which penetrates through said semiconductor substrate, said first insulation film and said second insulation film and which connects a predetermined terminal of said active element and said semiconductor substrate to each other.
13. A method for manufacturing a radio frequency monolithic integrated circuit as set forth in claim 12 , further comprising the steps of:
providing a groove which penetrates through said semiconductor substrate, said first insulation film and said second insulation film;
burying a polycrystalline semiconductor material containing an impurity in a high concentration into said groove; and
heat-treating said high-concentration impurity to diffuse said impurity into said semiconductor substrate.
14. A method for manufacturing a radio frequency monolithic integrated circuit as set forth in claim 12 , further comprising the steps of:
providing a recessed portion in said conductive substrate; and
bonding said semiconductor substrate to said conductive substrate provided with said recessed portion, with said first insulation film therebetween.
15. A method for manufacturing a radio frequency monolithic integrated circuit as set forth in claim 14 , further comprising the step of burying an insulating material in said recessed portion.