CN1510425A - Semiconductor thermocouple microwave power sensor - Google Patents

Abstract

The transducer consists of silicon substrate, N+ silicon under-impedance channel formed by diffusing N+ silicon in the substrate selectively, protective insulation layer prepared on the substrate, microwave absorption resistance set at the protective insulation layer and electrode leads for the first, the second as well as the third metal electrode. The trench which is in punch-through of the substrate and the protective insulation layer is made separately in between leads for the first, the second and the third electrode to form isolated thermocouple channel and isolated micro wave absorption channel in bridge shape.

Description

Semiconductor thermocouple type microwave power detector

Technical field

The present invention relates to a kind of microwave power detector that is used to carry out microwave power measurement, particularly relate to a kind of thermocouple type microwave power detector that is used to carry out microwave power measurement.

Background technology

Power measurement occupies extremely important status in electromagnetic measurement field.The sensing element that adopts in power measurement has thermistor, thermistor, sheet resistance, diode, thermal electric film, Hall element etc. multiple.The sensor of present domestic employing have only thermistor, thermal electric film etc. a few, exist problems such as poor reliability, precision is low, frequency band is narrow; That semiconductor thermocouple type microwave power detector has is highly sensitive, bandwidth, precision height, response are fast, good reliability, be easy to characteristics such as batch process, be widely used in the power meter of external import, 435A/8481A thermocouple wattmeter system as Hewlett-Packard Corporation's production, its principle is shown in Fig. 1 (a) and (b), and selectivity spreads N on P type silicon substrate 26 ⁺ Silicon 30, growth SiO on it ₂Or Si ₃N ₄As insulating protective layer 25, deposit Ta again ₂ N resistance film 2 and metal lead wire 1 and 6 form thermopair.N ⁺One end and the Ta of silicon 30 ₂The contact of N resistance, the hot junction 27 of formation thermopair, the other end contacts with metal lead wire 6, forms the cold junction point 28 of thermopair.Thermopair resistance is by N ⁺Sensistor and Ta ₂N resistance two parts are formed, and with Ta ₂N resistance is main.Microwave power is dispersed on the thermopair resistance, produces heat, makes the thermojunction temperature be higher than cold junction, produces thermoelectrical potential by Seebeck effect (thermoelectromotive force effect) on thermopair, and the size of this thermoelectrical potential is directly proportional with the microwave power that is absorbed.Go out microwave power by detecting the thermoelectrical potential value with regard to energy measurement.In order to reduce thermal losses,, thermopair is positioned on the thick silicon fiml of 5 μ m with P type silicon substrate thinning back side.The power input P of the sensitivity S unit of being defined as of thermopair microwave power detector ₀The thermoelectrical potential value U that produces, promptly

$s=\frac{U}{P_0}---\left(1\right)$

U=α Δ T, α is a Seebeck coefficient, Δ T is that the cold and hot junction temperature of silicon is poor, P=(1-r) Po, r is a reflectivity, and P is the thermopair power absorbed, and (1) formula can be written as:

$s=\frac{(1-r)\·\mathrm{\α}\·\mathrm{\ΔT}}{P}---\left(2\right)$

Δ T/P is that the cold and hot junction temperature that causes of unit absorbed power is poor, is inversely proportional to the heat conduction σ of thermocouple structure.Therefore,

$s.\∞(1-r)\·\mathrm{\α}\·\frac{1}{\mathrm{\σ}}---\left(3\right)$

The response time τ of thermocouple sensor is relevant with the thermal capacitance H of thermocouple structure and thermal conductance σ.

$\mathrm{\τ}=\frac{H}{\mathrm{\σ}}---\left(4\right)$

By (3) formula as can be known, improve sensitivity, can reduce reflectivity r, increase Seebeck coefficient α, reduce thermal conductance σ.By (4) formula, thermal conductance reduces to increase the time τ of response, so thermal capacitance H also should corresponding reducing, and is unlikely to degenerate with the response characteristic that guarantees sensor.

The Seebeck coefficient of silicon is relevant with its impurity concentration, and is also promptly relevant with its resistance.

$\mathrm{\α}=86.3(2+\ln \frac{2.5\×{10}^{19}}{n}+1.5\ln \frac{T}{300})---\left(5\right)$

Wherein, n is an impurity concentration, and T is an absolute temperature.By following formula as can be known, resistance is more little, and impurity concentration is high more, and Seebeck coefficient is just more little.Thermocouple structure (as shown in Figure 1) for film, for with the microwave input impedance matching, just must limit the resistance of thermopair all-in resistance, but so, the doping of silicon just can not be very little, otherwise sensistor can increase, and the temperature-coefficient of electrical resistance of silicon is bigger, under high-power situation, its changes in resistance can influence total thermopair resistance, causes impedance mismatching.Therefore, the sensitivity of this thermocouple wattmeter is not high.

Summary of the invention

The existence of problem in view of the above the purpose of this invention is to provide a kind of highly sensitive semiconductor thermocouple type microwave power detector that has.

Semiconductor thermocouple type microwave power detector of the present invention comprises: silicon substrate; Selectivity diffusion N in this this silicon substrate ⁺Silicon and the N that forms ⁺Silicon low impedance path; The insulating protective layer that on described silicon substrate, prepares; Be arranged on microwave absorbing resistance and first, second and the 3rd metal electrode lead-in wire on this insulating protective layer; Described N ⁺One end of silicon low impedance path links to each other with described the 3rd metal electrode lead-in wire by cold junction point, the other end links to each other with second metal electrode by hot junction microwave absorbing resistance, one end of described microwave absorbing resistance links to each other with described first metal electrode lead-in wire, and the other end links to each other with described second metal electrode lead-in wire; It is characterized in that: between described first, second and the 3rd metal electrode lead-in wire, have the groove of described silicon substrate of break-through and described insulating protective layer, make described microwave absorbing path and described thermocouple path become the catwalk of isolation.

And, semiconductor thermocouple type microwave power detector of the present invention, described microwave absorbing resistance preferably is limited on the miniature silicon island that is positioned at central area, described catwalk.

And semiconductor thermocouple type microwave power detector of the present invention, described hot junction are preferably disposed under the described microwave absorbing resistance and described N ⁺Silicon low impedance path directly contacts part.

And, semiconductor thermocouple type microwave power detector of the present invention, described microwave absorbing resistance is preferably Ta ₂N resistance.

And, semiconductor thermocouple type microwave power detector of the present invention, described insulating protective layer is preferably Si ₃N ₄, Al ₂O ₃Or SiO ₂Film.

According to semiconductor thermocouple type microwave power detector of the present invention; owing between first, second and the 3rd metal electrode lead-in wire, have the groove of break-through silicon substrate and insulating protective layer; make described microwave absorbing path and described thermocouple path become the catwalk of isolation; the heat flow path so can extend (thermocouple path); strengthen the length breadth ratio of heat flow path; increase thermal resistance; reduce the thermal capacity of heat conduction losses and thermopair; the thickness of control catwalk; can also control the thermal conductance and the thermal capacitance of thermopair, sensitivity and response time are optimized design.And, because microwave heat absorption path (microwave absorbing resistance) is separated from each other with thermopair path (detection thermocouple resistance), microwave absorbing resistance is made up of the microwave absorbing resistance with low resistance temperature coefficient fully, so can guarantee microwave absorbing resistance is complementary with the microwave input in bigger power bracket, thereby can improve the sensor standing-wave ratio (SWR), and can select thermopair resistance to adjust sensitivity neatly.Utilize semiconductor thermocouple type microwave power detector of the present invention, transducer sensitivity can be brought up to about 1000 μ V from about original 300 μ V.

And, because semiconductor thermocouple type microwave power detector of the present invention can so can make heat focus on the central area more, can further improve sensitivity with the microwave absorbing resistance limits on the miniature silicon island that is positioned at central area, described catwalk.

And, because semiconductor thermocouple type microwave power detector of the present invention can be arranged on hot junction under the described microwave absorbing resistance and described N ⁺Silicon low impedance path directly contacts part, so can increase conversion efficiency, shortens the corresponding time, further improves sensitivity.In addition, this structure can also reduce electromagnetic interference (EMI), increases the physical strength of chip.

Description of drawings

Following brief description accompanying drawing.

Fig. 1 is existing film-type semiconductor thermocouple type microwave power detector chip structure synoptic diagram, and wherein, Fig. 1 (a) is the front schematic view of chip, and Fig. 1 (b) is the horizontal section synoptic diagram of thermopair chip.

Fig. 2 is the structural representation of semiconductor thermocouple type microwave power detector chip of the present invention, and wherein, Fig. 2 (a) is the front schematic view of sensor chip; Fig. 2 (b) is the diagrammatic cross-section of sensor chip.

Embodiment

Fig. 1 is existing film-type semiconductor thermocouple type microwave power detector chip structure synoptic diagram, and wherein, Fig. 1 (a) is the front schematic view of chip, and Fig. 1 (b) is the horizontal section synoptic diagram of thermopair chip.Shown in Fig. 1 (a) and (b), selectivity diffusion N on P type silicon 8 substrates ⁺Silicon 30, growth SiO on it ₂And Si ₃N ₄As insulating protective layer 25, deposit Ta again ₂ N resistance film 2 and metal lead wire 1 and 6 form thermopair.N ⁺One end and the Ta of silicon 30 ₂The N contact, the hot junction 27 of formation thermopair, the other end contacts with metal lead wire 6, forms the cold junction point 28 of thermopair.Thermopair resistance is by N ⁺Sensistor and Ta ₂N resistance two parts are formed, and based on microwave absorbing resistance.Microwave power is dispersed on the thermopair resistance, produces heat, makes the thermojunction temperature be higher than cold junction, produces thermoelectrical potential by Seebeck effect (thermoelectromotive force effect) on thermopair, and the size of this thermoelectrical potential is directly proportional with the microwave power that is absorbed.Go out microwave power by detecting the thermoelectrical potential value with regard to energy measurement.

Fig. 2 is a semiconductor thermocouple type microwave power detector chip structure synoptic diagram of the present invention, has only a thermopair.Fig. 2 (a) sensor chip is a front schematic view; Fig. 2 (b) is the chip profile synoptic diagram.

As shown in Figure 2, selectivity diffusion N in silicon substrate 26 ⁺Silicon forms N ⁺Silicon low impedance path 30, preparation insulating protective layer 25 is selected Si on silicon substrate 26 ₃N ₄, Al ₂O ₃Or SiO ₂Film etc.; microwave absorbing resistance 24 and first metal electrode made from metal materials such as Au, Cu or Al 21, second metal electrode 22 and the 3rd metal electrode lead-in wire 23 are set on this insulating protective layer 25; one end of described microwave absorbing resistance 24 directly is connected with the outwardly directed elongated portion of first metal electrode lead-in wire 21; the other end directly is connected with the outwardly directed elongated portion of described second metal electrode lead-in wire 22; form the microwave absorbing path, its resistance is made of microwave absorbing resistance 24.Microwave absorbing resistance 24 is optional with the minimum tantalum nitride Ta of temperature-coefficient of electrical resistance ₂N material etc.Make N ⁺One end of silicon low impedance path 30 is connected with the 3rd metal electrode lead-in wire 23 by cold junction point 28, and the other end is by hot junction 27, and the part through microwave absorbing resistance 24 links to each other with second metal electrode 22 again, forms the thermocouple path.Adopt the MEMS technology that the monolithic film membrane of insulating protective layer 25 is removed the subregion; break-through silicon substrate 26 and insulating protective layer 25 form grooves 29 between described first, second and the 3rd metal electrode lead-in wire, make described microwave absorbing path and described thermocouple path become the catwalk of isolation.Microwave absorbing resistance 24 is limited on the miniature silicon island, links to each other by three Zhi Qiaoyu external circuit.

For semiconductor thermocouple type microwave power detector of the present invention, microwave power is imported from first metal electrode lead-in wire 21 by the co-planar waveguide on 7mm concentric cable and the jewel substrate (not shown), second metal electrode, 22 ground connection that go between, thereby heating microwave absorbing resistance 24, beneath silicon hot junction 27 temperature of microwave absorbing resistance are raise, between the cold thermocouple hot junction, produce temperature difference, and then generation thermoelectrical potential, promptly export the DC voltage that is proportional to the input microwave power between second metal electrode lead-in wire the 22 and the 3rd metal electrode lead-in wire 23 from the two ends of thermopair path, can realize microwave power measurement by detecting this thermoelectrical potential.

Semiconductor thermocouple type microwave power detector of the present invention is owing to adopted the MEMS technology that the monolithic film membrane of insulating protective layer 25 is removed the subregion; break-through silicon substrate 26 and insulating protective layer 25 form grooves 29 between described first, second and the 3rd metal electrode lead-in wire; make described microwave absorbing path and described thermocouple path become the catwalk of isolation; the heat flow path so can extend (thermocouple path); strengthen the length breadth ratio of heat flow path; increase thermal resistance, reduce the thermal capacity of heat conduction losses and thermopair.And the thickness of control catwalk can also be controlled the thermal conductance and the thermal capacitance of thermopair, and sensitivity and response time are optimized design.

And semiconductor thermocouple type microwave power detector of the present invention makes microwave absorbing resistance fully by the Ta with low resistance temperature coefficient because microwave heat absorption path (microwave absorbing resistance) and thermopair path (detection thermocouple resistance) are separated from each other ₂N resistance is formed, and is complementary with the microwave input in bigger power bracket so can guarantee microwave absorbing resistance, thereby can improves the sensor standing-wave ratio (SWR), and can select thermopair resistance to adjust sensitivity neatly.Utilize semiconductor thermocouple type microwave power detector of the present invention, transducer sensitivity can be brought up to about 1000 μ V from about original 300 μ V.

And, because semiconductor thermocouple type microwave power detector of the present invention can also so can make heat focus on the central area more, can further improve sensitivity with the microwave absorbing resistance limits on the miniature silicon island that is positioned at central area, described catwalk.

And, because semiconductor thermocouple type microwave power detector of the present invention can be arranged on hot junction under the described microwave absorbing resistance and described N ⁺Silicon low impedance path directly contacts part, so can increase conversion efficiency, shortens the corresponding time, further improves sensitivity.In addition, this structure can also reduce electromagnetic interference (EMI), increases the physical strength of chip.

And, the described miniature silicon island of semiconductor thermocouple type microwave power detector of the present invention can be designed to circle, square or other shapes, the Zhi Qiao that connects miniature silicon island also can be designed to different shapes, thickness and length breadth ratio, to strengthen the length breadth ratio of heat flow path, increase thermal resistance, reduce the thermal capacity of heat conduction losses and thermopair.

Embodiments of the invention more than have been described, but the present invention is not limited to above-described specific embodiment, every semiconductor thermocouple type microwave power detector that meets the various structures of purport of the present invention all should be thought to belong to scope of the present invention.

Claims (7)

1. a semiconductor thermocouple type microwave power detector comprises: silicon substrate (26); Selectivity diffusion N in this silicon substrate ⁺Silicon and the N that forms ⁺Silicon low impedance path (30); The insulating protective layer that on described silicon substrate, prepares (25); Be arranged on microwave absorbing resistance (24) and first metal electrode (21), second metal electrode (22) and the 3rd metal electrode lead-in wire (23) on this insulating protective layer;

One end of described microwave absorbing resistance (24) is connected with described first metal electrode lead-in wire, and the other end is connected with described second metal electrode lead-in wire, forms the microwave absorbing path; Described N ⁺One end of silicon low impedance path is connected with described the 3rd metal electrode lead-in wire by cold junction point (28), and the other end is by hot junction (27), and the part through microwave absorbing resistance (24) links to each other with described second metal electrode again, forms the thermocouple path; It is characterized in that:

Between described first, second and the 3rd metal electrode lead-in wire, have the groove (29) of described silicon substrate of break-through and described insulating protective layer, make described microwave absorbing path and described thermocouple path become the catwalk of isolation.

2. semiconductor thermocouple type microwave power detector according to claim 1 is characterized in that: described microwave absorbing resistance (24) is limited in being positioned on the miniature silicon island of central area, described catwalk.

3. semiconductor thermocouple type microwave power detector according to claim 1 and 2 is characterized in that: described hot junction (27) is arranged under the described microwave absorbing resistance (24) and described N ⁺Silicon low impedance path (30) directly contacts part.

4. semiconductor thermocouple type microwave power detector according to claim 1 and 2 is characterized in that: described microwave absorbing resistance (24) is Ta ₂N resistance.

5. semiconductor thermocouple type microwave power detector according to claim 1 and 2 is characterized in that: described insulating protective layer is Si ₃N ₄, Al ₂O ₃Or SiO ₂Film.

6. semiconductor thermocouple type microwave power detector according to claim 3 is characterized in that: described microwave absorbing resistance (24) is Ta ₂N resistance.

7. semiconductor thermocouple type microwave power detector according to claim 3 is characterized in that: described insulating protective layer is Si ₃N ₄, Al ₂O ₃Or SiO ₂Film.

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