KR19980032949A - Products containing TA oxide-based capacitive elements that are relatively unaffected by temperature - Google Patents

Abstract

Dielectric materials having a nominal composition of formula (Al ₂ O ₃ ) _x (Ta ₂ O ₅ ) _1-x , where x is greater than 0.03 and less than 0.15, unexpectedly have relatively small temperature changes in the dielectric constant (eg, Less than 50 ppm / ° C at 1 MHz and 20 ° C.) and relatively large dielectric constant values. The dielectric according to the invention is advantageously used in capacitive elements, for example MOS capacitors in integrated circuits for personal communication devices.

Description

Products containing TA oxide-based capacitive elements that are relatively unaffected by temperature

The present invention relates to Ta oxide based capacitive devices and articles comprising such devices.

For many technical fields (eg, personal communication devices for microwave frequencies), useful dielectric materials with high dielectric constant, low loss and low temperature constant of dielectric constant will be highly desired. The use of such dielectric materials facilitates the installation of resonator circuits, which are especially relatively insensitive to temperature.

Dielectric materials, typical Si-based oxides in use today, will eventually prove unsuitable for use in capacitors and other capacitive devices in integrated circuits due to their relatively low dielectric constant. Thus, more exotic genetic materials are under development.

Ta ₂ O ₅ is a particularly of interest dielectric material suitable for microelectronics manufacturing, forming a quality film under processing conditions that are compatible with microelectronics. However, Ta ₂ O ₅ has a relatively high temperature coefficient of dielectric constant, and consequently, Ta ₂ O ₅ -based capacitive elements have a significant dependence on the temperature of the capacitance. Capacitive element actually means a circuit element having capacitive characteristics. This includes capacitor filters and resonators.

To the temperature coefficient of the dielectric constant using a relatively low Ta ₂ O ₅ based dielectric material from other advantageous characteristics of the Ta ₂ O ₅ surface it is preferred. Such materials are described herein.

See K. Nomura et al., J. Electrochemical Society, Vol. 134, p. 922 (1987) report the deposition of composite thin films of Ta ₂ O ₅ and Al ₂ O ₃ and the specific properties of the composite films. Among these properties are capacitance and dispersion (see FIG. 5) as a function of frequency from 1 to 1000 kHz (see K. Nomura et al., J. Electrochemical Society, Vol. 138, p. 3701 (1991).

The invention is defined by the claims. The inventors have unexpectedly discovered that there is a relatively small composition range in which the dielectric constant temperature dependence of (Ta, Al) -oxide may be relatively lower than Ta oxide. For example, the temperature coefficient of Ta ₂ O ₅ is about 250 ppm / ° C at 1 MHz and 20 ° C, whereas the temperature coefficients of (Ta, Al) -oxide samples with an Al / (Al + Ta) atomic ratio of about 0.054 are the same. It is about -5 ppm / ° C under the conditions. This is very surprising, with considerable technical differences. The (Ta, Al) -oxide is a material consisting mainly of Ta, Al and oxygen, where Ta and Al are at least 90 (preferably 95) atomic percent of the total metal.

The addition of Al oxide not only significantly reduces the temperature dependence of the dielectric constant, but also increases the dielectric constant to some extent. In addition, the inventors have found that the dielectric constant of a material is nearly constant in the frequency range of about 1 kHz to 14 GHz and that the dispersion rate (Q) of the material is relatively low (eg, about 600 at 20 ° C. and 5 GHz).

Broadly, the present invention relates to products (e.g. ICs or personal communication devices) comprising capacitive elements that are relatively temperature independent.

More specifically, the article includes a capacitive device comprising a dielectric material comprising (Ta, Al) -oxide.

The Al / (Al + Ta) atomic ratio of the dielectric material is about 0.03 to 0.15 [the atomic ratio is selected so that the temperature coefficient of the dielectric constant of the dielectric material is low (eg, less than 50 ppm at 1 MHz and 20 ° C.). It is important.

The material may contain small amounts of any additives such as TiO ₂ and other metal oxides and Ta and Al together provide about 90 atomic percent of the metal content of the material.

1 shows exemplary data for the dielectric constant to Al / (A / + Ta) ratio x,

2 shows exemplary data on the temperature dependence of the dielectric constant as a function of x,

3 shows exemplary data on the frequency dependence of the dielectric constant and dispersion rate of an exemplary composition according to the present invention,

4 shows additional data on the temperature dependence of dielectric constant and dispersion rate,

5 to 7 are schematic views of capacitive elements according to the invention.

The dielectric material produced by the present study is a bulk sample with a nominal composition of formula (Al ₂ O ₃ ) _x (Ta ₂ O ₅ ) _1-x produced by ceramic processing technology. However, the present invention is not limited to this. For example, films with the same nominal composition are expected to have the same dielectric properties. Such films can be prepared directly from oxide targets or by various conventional techniques of oxidizing metal films. Among the common techniques are sputtering, chemical vapor deposition, laser ablation and beam evaporation. It is also contemplated that the dielectrics according to the present invention may contain relatively small amounts of metals other than Ta and Al. For example, it is known that the addition of a small amount (eg 8%) of TiO ₂ to Ta ₂ O ₅ can significantly increase the dielectric constant. Thus, the presence of TiO ₂ or other optical property improving components in the dielectrics according to the invention is envisaged.

Ceramic discs of nominal composition of formula (Al ₂ O ₃ ) _x (Ta ₂ O ₅ ) _1-x are mixed with high purity Ta ₂ O ₅ (99.993%) and Al ₂ O ₃ (99.99%) in the desired molar amounts. The mixture is prepared by heating in air at 1350 ° C. for 60 hours and then grinding by machine. The resulting powder is then heated to 1400 ° C. for 10 minutes, milled again, and then compacted into pellets 1/2 inch in diameter and 3 mm thick. The compacted pellets are placed in dense Al ₂ O ₃ plates on powders of the same composition and fired for 2 hours at 1575-1625 ° C. in air to densify. The resulting pellets are at least 90% of theoretical density. The process for preparing (Al, Ta) -oxides described above is an example and one skilled in the art will be able to employ the method in certain circumstances.

A multi-phase material is a powder X-ray thus produced in diffraction substance x is composed of 0 to 0.075 of Ta ₂ O ₅ solid solution and alumina content is high Ta ₂ O ₅ solid solution phase and x is 0.075 to 0.20 in AlTaO ₄ It can be seen that. One skilled in the art does not need to imply the presence of two oxides in the final product in which the formula (Al ₂ O ₃ ) _x (Ta ₂ O ₅ ) _1-x represents the starting composition (also called the nominal composition). Will know.

The flat surface of the ceramic pellets thus prepared was covered with 50:50 Ga-In alloy solder and brought into electrical contact. Commonly used impedance analyzers are used to measure dielectric constants (K) and dispersion rates (also referred to as tan δ and 1 / Q), which are between 1 kHz and 5 MHz at an electric field of about 5 V / cm and a temperature between −40 and 100 ° C.

FIG. 1 shows the dielectric constants at 1 MHz and 20 ° C. of an exemplary material having a nominal composition of formula (Al ₂ O ₃ ) _x (Ta ₂ O ₅ ) _1-x , where x is 0 to 0.20.

2 shows data for temperature dependence of dielectric constant for various exemplary samples. Curve 20 is associated with x = 0 and 0.025 and curves 21 through 24 are associated with x = 0.05, 0.075, 0.1 and 0.175, respectively. The curve for x = 0.2 is nearly identical to the curve for x = 0.175 below about 20 ° C., and nearly to the curve for x = 0.075 above about 20 ° C. The large difference in temperature dependence of the dielectric constant for x = 0 (and 0.025) and x0.03 is apparent from FIG. 2.

3 shows data for dielectric constant and dispersion as a function of frequency at 20 ° C. for an exemplary sample with x = 0.1. Curve 30 represents K from 1 kHz to 5 MHz, curve 31 represents D from 10 kHz to 5 MHz and curve 32 represents K from 1 to 14 GHz.

4 shows the observation that the detail of the temperature dependence of the dielectric properties of the material according to the invention depends in part on the preliminary situation. Curves 40 and 41 relate to a sample with x = 0.15 where curve 40 is associated with the sample after sintering at 1525 ° C. for 2 hours and curve 41 is sintered at 1575 ° C. for an additional 4 hours. It is related to a later sample. Curves 42 and 43 relate to a sample with x = 0.056 where curve 42 relates to the sample after sintering at 1625 ° C. and curve 43 is associated with the sample after sintering at 1100 ° C. for an additional 5 hours. Related. 4 shows K values (K ₂₀ ) and D values (D ₂₀ ) at 20 ° C. for the same sample and treatment conditions at 20 ° C. FIG.

The exemplary data in FIG. 4 clearly shows the dependence on the processing details of the dielectric properties of the material according to the invention and it is proposed that the dielectric properties can be modified for various applications.

Table 1 summarizes the dielectric properties as a function of the nominal composition. From the data, it can be seen that in the case of approximately 0.06 ≦ x0.15, the dielectric constant is slowly improved compared to Ta ₂ O ₅ at all temperatures. The exact value of the observed dielectric constant varies somewhat (~ +/- 5 to 10%) from manufacture to production due to differences in pellet density and orientation of the desired ceramic granules, but generally the gentle increase in K observed is constant. In addition, the material exhibits a consistently low D value, which results in a higher Q value. D was also found to vary somewhat with sample operating conditions. The low D values (0.0002 to 0.0005, Q = 5000 to 2000) in the table can be regarded as the upper limit of the intrinsic loss rate of the material at the MHz frequency since the measured values are not corrected for the distribution from the measurement circuit. Therefore, these materials can be said to be high quality dielectrics in the studied frequency range and beyond.

Table 2 shows the temperature coefficients (TCK) of the dielectric constants K and K for the exemplary samples (x = 0 to x = 0.2). TCK is defined as {(K ₁₀₀ -K _-40 ) / K ₂₀ } / 140 ° C, where K ₁₀₀ , K _-40 and K ₂₀ are K at 100 ° C, -40 ° C and 20 ° C, respectively.

Temperature coefficient of dielectric constant of formula (Al ₂ O ₃ ) _x (Ta ₂ O ₅ ) _1-x polycrystalline sample at ₁ MHz x K ₂₀ TCK (ppm / ℃) 0.0 33.08 +250 0.025 30.25 +270 0.05 30.39 +13 0.054 34.27 -5 0.056 39.50 -20 0.06 37.28 -33 0.075 39.99 -19 0.10 41.67 -42 0.125 37.10 -25 0.15 33.77 -19 0.175 29.19 -30 0.20 24.99 -21

As can be readily seen from Table 2, TCK is a relatively small value at a larger x value (e.g. about 250 ppm / ° C) at a value of x = 0 to a small value (e.g. -0.025). (Eg, about 20 ppm / ° C). The TCK of materials of x = 0.05 to 0.06 is particularly low, with the TCK typically varying sinusoidally in this range.

In view of the overall properties, it can be seen that compositions having x of about 0.03 to 0.15 have advantageous properties. This is an unexpected result, which, to the knowledge of the inventors, has not been proposed by the prior art, and materials having a composition in the recited range according to the invention include capacitive elements such as independent or integrated capacitors, filters, resonators and integrated capacitors. It can be advantageously used for a large number of products, especially those intended to be operated at a wide range of temperatures.

5 is a schematic diagram of an exemplary capacitive element 50 according to the present invention, i.e., an independent capacitor, wherein 51 to 54 respectively show an upper electrode, a lower electrode, a dielectric and an encapsulating material according to the present invention. Except for the novel dielectric, capacitor 50 may be conventional.

6 is a schematic view of a further capacitive element, i.e., an integrated MOS capacitor 60, according to the present invention, wherein 61 to 63 each represent a (typically doped) semiconductor substrate, a dielectric layer and an electrode according to the present invention. Indicates. Except for the novel dielectric, capacitor 60 may be conventional.

7 is a schematic view of a further capacitive element 70 according to the present invention, ie a split ring resonator 71, in which the dielectric 72 is disposed in the hole of the resonator. Split ring resonators are known. The member 72 is made of a dielectric material according to the present invention to increase capacitance and temperature safety. Many resonators can be assembled into a filter as known to those skilled in the art.

Independent and integrated circuits according to the invention are advantageously used, for example, in communication devices and the exemplary resonators and filters according to the invention are used as base stations or repeaters in wireless communication systems.

Claims (6)

The Al / (Al + Ta) atomic ratio of the dielectric material (which is selected so that the absolute value of the temperature coefficient of the dielectric constant of the dielectric material is less than 50 ppm / ° C at 1 MHz and 20 ° C) is about 0.03 to 0.15 and Al and Ta are A capacitive element comprising (Ta, Al) oxide comprising a dielectric material 53 having a dielectric constant and a temperature coefficient of dielectric constant, characterized in that it together provides at least 90 atomic% of the total amount of metal in the dielectric material : 50]. The article of claim 1, wherein the ratio is selected such that the absolute value of the temperature coefficient is less than 20 ppm / ° C. at 1 MHz and 20 ° C. 7. The article of claim 1 wherein Al and Ta provide at least 95 atomic percent of the total amount of metal. 4. The article of claim 3 wherein Al and Ta essentially provide the total amount of metal. The article of claim 1, wherein the capacitive element comprises a first capacitive member and a second capacitive member with a layer of dielectric material disposed between the capacitive members. The article of claim 1, wherein the capacitive element comprises a resonant resonator element with a gap between the dielectric element and the dielectric member.