News Column

Patent Issued for Tunable Capacitor

July 16, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- NXP, B.V. (Eindhoven, NL) has been issued patent number 8767373, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Furukawa, Yukiko (Kimitsu, JP); Reimann, Klaus (Eindhoven, NL); Jedema, Friso Jacobus (Eindhoven, NL); Tiggelman, Markus Petrus Josephus (Eindhoven, NL); Roest, Aarnoud Laurens (Geldrop, NL).

This patent was filed on April 29, 2009 and was published online on July 1, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Several types of tunable capacitors have been developed for mobile communication applications such as tunable filters, phase shifters, multiplexers, voltage-controlled oscillators and tunable matching networks.

"A first type is a semiconductor based tunable capacitor, i.e. PIN diodes, varactor diodes and field-effect transistors (FET's). A second type is a MEMS type tunable capacitor, which has a possibility to gain a large change of capacitance due to change of a distance between electrodes or in plane relative position of the electrodes (an in-plane translation of the bottom or top electrode may result in a change of the effective overlapping area of the capacitor and thus vary the capacitance). A third type is a tunable capacitor using ferroelectric material sandwiched between two electrodes. In that type of capacitor the relative dielectric constant of the ferroelectric material is varied by applying an electric field (which is done by applying a voltage over the electrodes). All three types of tunable capacitors have their own limitations in operational use.

"In view of these limitations there is a need for an alternative type of tunable capacitor."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "It is an object of the invention to provide an alternative tunable capacitor.

"The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

"In a first aspect, the invention relates to electronic device having an operation temperature range, the electronic device comprising:

"a tunable capacitor comprising a first electrode, a second electrode, and a dielectric arranged between the first electrode and the second electrode, wherein the dielectric comprises dielectric material having a value of a relative dielectric constant (.di-elect cons.r) varying at least within the operation temperature range, and

"a temperature varying means being thermally coupled to the tunable capacitor for providing a temperature of the dielectric causing a predetermined capacitance of the tunable capacitor.

"The effect of the features of the electronic device in accordance with the invention is that a temperature-dependence of the relative dielectric constant of a dielectric material is exploited for creating a tunable/controllable capacitance. The temperature varying means sets a temperature of the dielectric and subsequently the capacitance of the capacitor assumes a value corresponding with that temperature. In other words, the invention provides a tunable capacitor which exploits temperature dependence of the relative dielectric constant for varying the capacitance, which is an alternative to the known tunable capacitors in which parameters like electrode distance dependency and electric field dependencies are used.

"The earlier mentioned different types of tunable capacitors, together with their advantages and disadvantages, are discussed in the following scientific publication:

"Marsan, E.; Gauthier, J.; Chaker, M.; Ke Wu, 'Tunable microwave device: status and perspective', IEEE-NEWCAS Conference, 2005. The 3rd International, Volume/Issue, 19-22 Jun. 2005, p. 279-282. The semiconductor based tunable capacitors generally have a high tuning ratio (which is defined as the maximum achievable capacitance divided by the minimum achievable capacitance), a fast response time. However, their Q-factor is moderate and their power consumption is poor. The MEMS type tunable capacitors generally have a very high Q-factor and have excellent power consumption (extremely low). However, their tuning ratio is low and their response time is slow. The ferroelectric tunable capacitors have a relatively high (up to 3.5) tuning ratio, an excellent power consumption (extremely low), and a very fast response time. However, their Q-factor is moderate.

"The inventors have identified further drawbacks in the MEMS type tunable capacitors, namely that they actually require an actuator to be controlled and, in order to achieve an electrostatic force which is larger than the mechanical forces a relatively big size of the actuator is required. A further drawback of the ferroelectric tunable capacitors, identified by the inventors, is that their tuning ratio is still relatively small. They have identified a need for much larger tuning ratios. In the discussion of the embodiments of the invention these issues will be, where applicable, further discussed because the invention creates new possibilities.

"In an embodiment of the electronic device of the invention the temperature varying means comprises a resistive element for carrying a current to set the temperature. A resistive element carrying a current is a convenient means for heating the dielectric material and thereby varying the relative dielectric constant, because the current through the resistive element can be easily controlled. In a thermal system a predefined current strength will (after settling) result with a predefined temperature of the dielectric material. Consequently, this temperature will then comply with a predefined relative dielectric constant and a capacitance.

"An embodiment of the electronic device of the invention further comprises a controller being coupled to the resistor and being arranged for controlling the temperature of the dielectric by steering the current through the resistive element. The use of a controller that steers a current through the heater enables a more accurate setting of the temperature, and also it enables more flexibility in varying the tunable capacitor over time. The controller may be part of a control system.

"An embodiment of the electronic device of the invention further comprises a temperature sensor for measuring an actual value of the temperature of the dielectric material, wherein the controller is arranged for receiving from the temperature sensor a temperature signal indicative for the actual value of the temperature, the controller being further arranged for receiving a desired temperature signal indicative for a desired temperature, and wherein the controller is arranged for controlling the temperature to decrease an absolute difference between the temperature signal and the desired temperature signal. This embodiment constitutes a first example of a control system. In this embodiment a temperature error signal is determined and used for controlling the temperature.

"An embodiment of the electronic device of the invention further comprises capacitance measurement circuitry for measuring an actual value of the capacitance, wherein the controller is arranged for receiving from the capacitance measurement circuitry a capacitance signal indicative for the actual value of the capacitance, the controller being further arranged for receiving a desired temperature signal indicative for a desired capacitance, and wherein the controller is arranged for controlling the temperature to decrease an absolute difference between the capacitance signal and the desired capacitance signal. This embodiment constitutes a second example of a control system. In this embodiment a capacitance error signal is determined and used for controlling the temperature.

"In an embodiment of the electronic device of the invention the dielectric comprises ferroelectric material which exhibits a phase transition from a ferroelectric phase to a paraelectric phase in a temperature range from -50.degree. C. to 250.degree. C. Ferroelectric materials are known to have a relatively large temperature dependency of their relative dielectric constant. Especially those ferroelectric materials which show a phase transition and in particular in the temperature range from -50.degree. C. to 250.degree. C. are of interest, because this temperature range coincides with the operation temperature range. The dependency may be large both in absolute as well as relative terms. The absolute variation is the maximum relative dielectric constant achievable within the operation temperature range divided by the minimum relative dielectric constant achievable within the operation temperature range. A large relative temperature dependency means a large variation of the relative dielectric constant per degree Celsius (the derivative of the temperature dependency). Depending on the application one or both of these variations may be used. When the ferroelectric material exhibits a phase transition from a ferroelectric phase to a paraelectric phase this generally coincides with a very strong increase of the relative dielectric constant. The temperature at which this happens is also called the Curie temperature (Tc). Consequently, a very strong increase of the capacitance may be observed, which also means an extremely large tuning ratio which is much larger than what may be achieved with the known types of tunable capacitors. Another great advantage of a large dielectric constant is that the capacitor may be designed much smaller, which is a great advantage over the known tunable capacitor types. In order to be able to use this effect the temperature at which this phenomenon is observed lies preferably within or close to the operation temperature range of the electronic device, i.e. in the range from -50.degree. C. to 250.degree. C.

"In an embodiment of the electronic device of the invention the ferroelectric material exhibits a phase transition from a ferroelectric phase to a paraelectric phase in a temperature range of 50.degree. C. to 150.degree. C. When the phase transition of the ferroelectric material occurs in the sub-range from 50.degree. C. to 150.degree. C., which coincides with the upper part of a conventional operation temperature range of an electronic device, it requires less effort (energy) to vary the capacitance of the capacitor. This feature generally implies that the temperature varying means only needs to heat (and not cool) the dielectric material with respect to the environment. A resistive element may be used as heater in that case. In a physical environment having a certain heat loss, cooling may be simply achieved with a heater by heating to a less extent (i.e. a smaller current through the resistive element).

"In an embodiment of the electronic device of the invention the dielectric comprises ferroelectric dielectric material selected from a number of groups comprising: a tungsten-bronze group comprising K.sub.3Li.sub.2Nb.sub.5O.sub.15 and Ba.sub.2NaNb.sub.5O.sub.15, a KDP group comprising KH.sub.2PO.sub.4, KD.sub.2PO.sub.4, RbH.sub.2PO.sub.4, and KH.sub.2AsO.sub.4, a LiNbO.sub.3 group comprising LiNbO.sub.3 and LiTaO.sub.3, and a Perovskite group comprising BaTiO.sub.3, PbTiO.sub.3, and KNbO.sub.3, and a Pb.sub.5Ge.sub.3O.sub.11 group. These groups of ferroelectric materials have been identified by the inventors as exhibiting a significant variation of their relative dielectric constant with the temperature, wherein the respective ranges in which the most significant variation (and Curie temperatures) is seen are distributed over a range from -200.degree. C. to 1300.degree. C. Depending on the application a different material may be selected from these groups.

"In an embodiment of the electronic device of the invention the dielectric material comprises material from the Perovskite group that complies with the following chemical formula: XYO.sub.3, wherein X comprises and least one of Ba, Pb, Sr, Ca, and wherein Y comprises at least one of Sn, Hr, Zr, Ce, Ti, and Th. These Perovskite materials have been identified by the inventors, at least so far, to exhibit the strongest temperature dependence of their relative dielectric constant. The highest tuning ratio may be achieved using these materials.

"In an embodiment of the electronic device of the invention X comprises Ba.sub.1-x-ySr.sub.xPb.sub.y with 0.ltoreq.x

"In an embodiment of the electronic device of the invention Y comprises at least Ti.sub.1-zZr.sub.z with 0.ltoreq.z.ltoreq.1. When starting from XTiO.sub.3 material, the addition of zirconium (Zr) increases the peak value of the relative dielectric constant at the Curie temperature (Tc) and also broadens the peak. This mechanism may be used to tune the relative dielectric constant dependency to a desired dependency.

"In a second aspect the invention relates to semiconductor device comprising the electronic device in accordance with the invention. When the electronic device is integrated with in a semiconductor device it may be advantageously integrated with electronic circuits.

"An embodiment of the semiconductor device of the invention comprises a substrate with insulating material provided at a surface thereof, wherein the capacitor and the heater are arranged within the insulating material, and wherein the capacitor and the heater are thermally coupled to each other. In such a structure it is easy to control the temperature of the capacitor (and thereby the dielectric material). In practice, a substrate, for example a semiconductor substrate with an integrated circuit at a surface thereof, often comprises an insulating material by itself, for example in the back-end-of-line stack.

"In an embodiment of the semiconductor device of the invention the insulating material comprises a cavity in which the capacitor and the heater are both arranged. When the heater and the capacitor are arranged in a cavity with for example air inside a system is created with very low heat loss. A lower heat loss will lead to a faster tunable capacitor as the temperature will settle much faster. A large heat loss enables to cool the material fast, however maintaining a temperature requires more energy.

"In a third aspect the invention relates to an electronic circuit comprising the electronic device in according with the invention. Preferably, the electronic circuit is selected from a group comprising: tunable filter, phase shifter, multiplexer, voltage-controlled oscillator, and tunable matching network. Tunable capacitors have a very wide scope of application. The circuits mentioned here, are just a selection of some important ones.

"In a third aspect the invention relates to a method of manufacturing an electronic device, wherein the method comprises steps of:

"providing a tunable capacitor comprising a first electrode, a second electrode, and a dielectric arranged between the first electrode and the second electrode, wherein the dielectric comprises dielectric material having a value of a relative dielectric constant (.di-elect cons.r) varying at least within the operation temperature range, and

"providing a temperature varying means being thermally coupled to the tunable capacitor for providing a temperature of the dielectric causing a predetermined capacitance of the tunable capacitor. The advantages of the method and its embodiments follow that of the corresponding electronic device.

"These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter."

For the URL and additional information on this patent, see: Furukawa, Yukiko; Reimann, Klaus; Jedema, Friso Jacobus; Tiggelman, Markus Petrus Josephus; Roest, Aarnoud Laurens. Tunable Capacitor. U.S. Patent Number 8767373, filed April 29, 2009, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8767373.PN.&OS=PN/8767373RS=PN/8767373

Keywords for this news article include: NXP B.V., Electronics, Semiconductor.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Electronics Newsweekly


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters