Patent Description:
Many applications involve heating. Efficiency, precise control, convenience, size, and usability can be concerns with existing techniques for establishing or adjusting temperature of a target object or space.

<CIT>) provides a self-regulating heater using a semiconductor as a heating element that has a fast response and is temperature limited. A biasing network operates the semiconductor to cause the semiconductor to conduct more current at lower temperatures and less current at higher temperatures. Spetz uses a field-effect transistor (FET) as a heat source and then drains the resulting current out the FET in a loop around the semiconductor in order to complete the circuit for the pass-through current.

<CIT>) discusses an example of applying microwaves to a semiconductor wafer to heat the semiconductor wafer. Wander uses a microwave cavity as the energy source, and merely places the semiconductor in the cavity as a bulk target to be heated, without providing any ability to localize heat production or gradients at one or more particular locations within the semiconductor substrate.

<CIT>) describes regional heating of a system having a substrate. The method includes applying a thin film to the system, and controllably energizing a coil positioned near the thin film. The energized coils generate a magnetic flux to induce a current in the thin film thereby heating the system.

Patent Publication <CIT>) describes a heating apparatus with a surface acoustic wave generator. The surface acoustic wave generator may have a piezoelectric substrate and inter-digital transducers (IDT) formed on the piezoelectric substrate, and a thermal reaction part is formed at the part of the piezoelectric substrate.

Patent Publication <CIT>) describes a semiconductor device that warms a surface of a living body required to be warmed at an appropriate timing without causing low temperature burns. A sheet having a heat generating function including a circuit capable of receiving electric power without contact over a sheet containing plastic or a fibrous body, a heat generating circuit, and a circuit that controls the temperature of the heat generating circuit is manufactured. The user with the sheet transmits the radio signal from the transmission device outdoors or indoors to heat the heat generating circuit on the sheet and the heat can be conducted to the skin of the user. Temperature can be automatically adjusted by the circuit for controlling the temperature of the heat generating circuit.

Patent Publication <CIT>) concerns an RF electrode set for renal nerve ablation. A catheter is provided with a treatment element at its distal end. A multiplicity of electrodes are spaced apart on the treatment element and configured for switchable activation and deactivation in a predetermined sequence to generate overlapping zones of heating directed at perivascular nerves of the renal artery.

The present inventor has recognized a need for improved techniques for establishing or adjusting temperature of, or temperature gradient in, a semiconductor, thin-film metal, or other substrate (or, indirectly, that of another object or space that is thermally coupled to the semiconductor substrate). In this document, the term "substrate" includes the layer of material that is actively excited through a non-zero frequency time-varying electric field, and can include a semiconductor substrate, a thin-film or other metal substrate, a quartz substrate, a diamond substrate, or other suitable substrate material or composite material. In an illustrative but non-limiting example, the non-zero frequency time-varying electric field can be capacitively coupled to a semiconductor substrate, but such coupling and such a substrate are not requirements for certain aspects of the present subject matter.

This document describes, among other things, techniques for providing controlled time-varying excitation of a semiconductor material, such for producing thermal energy in the semiconductor material. A non-zero frequency time-varying electric field can be capacitively applied (in an illustrative, non-limiting example), such as via local electrodes, to the semiconductor material. The frequency can be adjusted, such as to a desired degree of excitation, such as to induce majority carriers in the semiconductor to oscillate to generate heat. Other techniques for introducing energy into the semiconductor may be used in combination with such a technique. Such localized heat production in time and space can permit control or management of one or more temperature gradients in the semiconductor substrate.

The invention is an apparatus and a method as defined in claim <NUM> and claim <NUM>. Embodiments of the invention are presented in the dependent claims.

In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components.

This document describes examples of improved techniques for establishing or adjusting temperature of a semiconductor or other suitable substrate (or, indirectly, that of an object or space that is thermally coupled to the substrate) such as for establishing or adjusting one or more temperature gradients in the substrate.

In an illustrative, non-limiting example, the present techniques can turn a semiconductor substrate into a heat source, such as by capacitively applying a radiofrequency (RF) or microwave or other time-varying frequency source as the input energy. This can permit localized heat production, controllably variable heat production, multi-mode control of the localized heat production, and efficient heat generation. Localized heating can further enable establishing and managing one or more temperature gradients in the substrate, such as in time or space, or both.

The present techniques can use a semiconductor substrate, or one or more other materials with free charge carriers that can remain confined within the substrate, for producing thermal energy-which is different from the waste thermal energy produced by a typical semiconductor logic or other integrated circuit chip, which requires pass-through current.

For example, unlike a digital or analog semiconductor integrated circuit, the present localized heat generation apparatus and methods need not require an electrically conductive connection to power and ground, although such power and ground inputs can be included for use with other electrical circuits that can optionally be included on the same integrated circuit as the present localized heat generation apparatus. By contrast, a typical digital or analog semiconductor integrated circuit will require logic gate circuits and electrically conductive power and ground connections.

In an example of using the present techniques, the RF or other time-varying frequency energy can be transferred to the semiconductor or other substrate through capacitive contacts (in an illustrative non-limiting example). The resulting process can be conceptualized as an input conduction current, which leads to a displacement current in the first capacitive electrode contact, and conduction current in the substrate, a displacement current in the second capacitive electrode contact, and finally a conduction current out of the second electrode to the voltage source. Displacement current is only generated at the capacitor contacts when an alternating voltage of nonzero frequency is applied. An oscillating conduction current in the substrate is created when the excitation is an alternating voltage of nonzero frequency. When viewed from a particle physics perspective, the charged particles in the substrate are confined to the body of the substrate and do not physically leave the substrate through the capacitive contacts. The continuity condition for current means that the displacement current in the capacitor is equal to the conduction current in the substrate. In the present approach, when using a semiconductor substrate, heat is generated by inelastic collision of the majority carriers confined within the semiconductor substrate with the semiconductor lattice and heat conduction is by the semiconductor lattice. In the present approach, when using a thin-film metal or other metal substrate, the heat is carried by majority carriers moving in the thin film metal or other metal substrate.

The present techniques can allow multi-mode control of thermal energy production and the establishment of one or more thermal gradients at desired locations in the substrate. Thermal energy production in the semiconductor material can be accomplished by altering energy input of the time-varying electric field. In a first mode, this can be achieved by specifying or managing the spacing between electrodes, and/or managing the inductance between the electrodes either by tuning the spacing or through external circuits connected to the electrodes that can be used to capacitively apply a time-varying frequency to the semiconductor. A second mode can control thermal energy production by establishing or adjusting the frequency of the time-varying electrical signal that is capacitively or otherwise applied to the semiconductor or other substrate. A third mode can control thermal energy production by adjusting the amplitude of the time-varying electrical signal that is capacitively or otherwise applied to the semiconductor or other material. Two or more of these modes can be used in combination with each other, or with one or more other adjunct modes.

One or more thermal energy gradients can be established in the semiconductor substrate using one or multiple techniques. For example, adjusting the frequency of the time-varying electrical signal being capacitively or otherwise applied to the semiconductor or other substrate via the electrodes can change a matching or coupling efficiency using such electrodes, which, in turn, can establish or control one or more thermal gradients. The "match" between the applied time-varying electrical signal and the electrodes is a function of both the frequency of the applied time-varying electrical signal and the spacing between electrodes at one or more locations on such electrodes. Variable thermal energy production with a particular pair of electrodes can be used to establish or adjust a localized thermal energy gradient in the semiconductor substrate, such as by specifying or adjusting a spacing between the electrodes (or respective nearest or other portions thereof) being used to capacitively input the time-varying electrical signal. Variation in spacing between locations on respective electrodes can be used to create a variable frequency match, for a particular input frequency, such as along the axis or length of the electrodes (see, e.g., spacing "S" and axis "Y" in <FIG>). This can provide variable energy deposition along the axis of the electrodes and, consequentially, a temperature gradient along the axis of the electrodes.

Once the electrodes are in place, the spacing or geometry will remain constant. Further control of the temperature gradient can be established by altering the frequency of the time-varying electrical signal being applied to the electrodes. The temperature gradient is a consequence of a distribution of thermal energy bands, and associated underlying current bands, between the electrodes or between respective locations on the respective electrodes.

In an example, a frequency change of the applied electrical energy can create a "step function" in the temperature gradient, in which the overall spatial temperature gradient can remain the same in response to the frequency change, but in which the temperature values of the maximum and minimum temperatures in the spatial temperature gradient change in response to the change in the applied frequency. The step function in the spatial temperature gradient can match to the average or lumped impedance between the traces or electrodes, which can be treated as a single lumped system. In a serpentine or variable-spacing electrode geometry, it is possible that certain locations on the electrode get "turned off," because no match exists at the applied frequency for such locations, therefore, no current or heat is generated at such locations. <FIG> illustrates an example of step function control.

In an example, a frequency change of the applied electrical energy can additionally or alternatively alter the spatial temperature gradient by altering the spatial distribution of the thermal and underlying current bands between respective locations on the respective electrodes. In an example, such altering the spatial distribution of the temperature gradient can include altering the locations of the maximum and minimum temperatures, e.g., shifting along the Y-axis. <FIG> illustrates an example of such a frequency change altering a spatial distribution of the temperature gradient, such as can include altering the locations of the maximum and minimum temperatures by shifting along the Y-axis. Without being bound by theory, it is believed, based on current theory and similar applications, that frequency control may be capable of controlling the match at individual points of the electrodes along the Y-axis.

The ability to establish spatial temperature gradient variations can be desirable for certain applications. Depending on the geometry and size of the electrodes, it may not be always be possible to recognize the minute changes in spatial temperature gradients, making step function control preferred as a practical way to adjust or control such temperature gradients.

In the third technique, the frequency of the time-varying electrical input signal can be altered, such as to enable a partial impedance match the between the electrodes to obtain the requisite energy input for obtaining the desired localized thermal energy output in the substrate. In sum, multi-modal control of localized and variable thermal energy production in the semiconductor substrate is possible.

The present approach to localized heating is believed to be more efficient than heating a semiconductor within a microwave cavity. In cavity heating efficiency depends on the ratio of the size of the cavity and the target semiconductor. By contrast, the present approach requires no cavity and offers a way to access the semiconductor continuously, such as for using the semiconductor as an active heat source, rather than just a target object to be heated.

<FIG> shows an example of a heating or other temperature adjustment system <NUM>. In an example, the system <NUM> can include a silicon, germanium, gallium arsenide or other semiconductor substrate <NUM> (or other non-semiconductor substrate material, as explained elsewhere herein). The semiconductor substrate <NUM> can include one or more of a bulk semiconductor, a semiconductor wafer, a diced or other portion of a semiconductor wafer, etc..

Two or more electrodes 104A-B can be located indirectly on the semiconductor substrate <NUM>. The electrodes 104A-B are located so as to be physically separated from each other. Such separation can include a region of the semiconductor substrate <NUM> generally located at least partially between the electrodes 104A-B. In an example, the electrodes 104A-B can include metal or other electrically conductive signal traces. Such conductive signal traces can be indirectly located on the semiconductor substrate <NUM>, for example, such as separated therefrom by an intervening insulator or dielectric layer, such as silicon dioxide, silicon nitride, or the like. Such separation from the semiconductor substrate <NUM> by an intervening dielectric layer can permit, in an example, capacitive coupling of a non-zero frequency time-varying electric field signal on the electrodes 104A-B to the semiconductor substrate <NUM>. The electrodes 104A-B are configured to receive the time-varying electrical energy, such as can include an externally regulated and applied non-zero frequency, such as for creating a resulting time-varying electric field in the semiconductor substrate <NUM>, such as for establishing or adjusting a local temperature of the portion of the semiconductor substrate <NUM> that is located in a vicinity between or near the electrodes 104A-B.

A temperature sensor <NUM> can be integrated into, formed upon, placed near, or otherwise located in association with the semiconductor substrate <NUM> or an object or space to be heated by the semiconductor substrate, such as to sense a temperature thereof. Information representative of the temperature of the semiconductor substrate <NUM> can be provided by the temperature sensor <NUM>, such as to a control circuit <NUM>. The control circuit <NUM> can be configured to control an electric field signal generator <NUM>, such as for use in closed-loop or other control of the frequency, amplitude, or other operation of the electric field signal generator <NUM>. In an illustrative example, the temperature sensor <NUM> can include a pn junction diode integrated into the semiconductor substrate <NUM>. This can provide a resulting temperature-dependent reverse-bias pn junction diode current signal. This resulting signal can be signal-processed, such as by the control circuit <NUM>, such as to provide a resulting temperature-dependent control signal to the electric field signal generator <NUM>, such for use to adjust an output frequency or amplitude or impedance matching of the electric field signal generator <NUM>, such as to establish or adjust a temperature of the semiconductor substrate <NUM> or a localized portion thereof.

The electric field signal generator <NUM> can include a signal generator (source) and can optionally include an impedance matching circuit. The electric field signal generator <NUM> can be operatively coupled to the electrodes 104A-B, such as by using a wired or at least partly wireless connection 110A-B, such as to deliver a time-varying electric field signal to the electrodes 104A-B. The time-varying electric field signal received by the electrodes 104A-B from the electric field signal generator <NUM> can be used to apply an AC electric field, e.g., a time-varying electric field having non-zero frequency, to a portion of the semiconductor substrate <NUM>, such as to provide a resulting displacement current to the portion of the semiconductor substrate <NUM>, such as to trigger heating or otherwise establish or adjust a temperature of the portion of the semiconductor substrate <NUM>, and without requiring indirect heat coupling passing heat through the dielectric to the semiconductor substrate <NUM>.

Heating the semiconductor substrate <NUM> by localized capacitively-coupled application of a non-zero frequency time-varying electric field does not require a net charge flowing into or out of the semiconductor substrate. Without being bound by theory, it is believed that the present approach of applying non-zero frequency time-varying electric field can induce particle motion such that majority carriers in the semiconductor substrate <NUM> can oscillate bidirectionally (e.g., back-and-forth) at the applied frequency with respect to the lattice of the semiconductor substrate. This is believed to produce phonons that vibrate periodically in harmonic motion proportional to the oscillating displacement current. By controlling the frequency of the non-zero frequency applied time-varying electric field, the majority carrier oscillation can be controlled which, in turn, can control phonons and heat generation.

Such heating the semiconductor substrate <NUM> using the displacement current by the present approach of applying a non-zero frequency time-varying electric field is also different from inductive heating in that, unlike inductive heating, no magnetic field need be applied. No magnetic-field induced eddy currents in the semiconductor substrate <NUM> need be created. No loop or electromagnet is required to establish a magnetic field in the semiconductor substrate.

Information about the temperature of the semiconductor substrate <NUM>, such as sensed by the temperature sensor <NUM>, can be used to control at least one of the amplitude or the frequency of the electric field generated by the electric field signal generator <NUM> and provided by the electrodes 104A-B to the semiconductor substrate <NUM>, and can additionally or alternatively be used to turn the applied electric field on or off, such as at a desired duty cycle to attain or maintain a target temperature of the semiconductor substrate <NUM>, or a target temperature of an object or space to be heated by the semiconductor substrate <NUM>.

Adjusting the non-zero frequency of the applied time-varying electric field can affect a coupling of the time-varying electric field to the semiconductor substrate <NUM> and, therefore, can be used to control the conversion of the applied electric field into heating of the semiconductor substrate <NUM>. The applied frequency manifests itself as the oscillating frequency of the particles inside the substrate. The applied frequency can range (e.g., depending on the application) such as all the way from a low frequency, for example, such as near-DC, a <NUM> line frequency, up to a frequency in a radio frequency (RF) or microwave or TeraHertz (THz) frequency range, or beyond. Additionally or alternatively, adjusting the amplitude of the applied electric field can affect the power of the electric field to the semiconductor substrate <NUM> and, therefore, can be used to control the conversion of the applied electric field into heating of the semiconductor substrate <NUM>. Additionally or alternatively, one or more constructive or destructive interference or duty cycle or other technique can be used, such as to control an amplitude of the applied non-zero electric field at a desired location or region of the semiconductor substrate <NUM>.

In an example, the two or more electrodes 104A-B shown in <FIG> can include parallel straight linear metal strip segments, such as can be located on the same side of the bulk semiconductor substrate <NUM>, but separated therefrom by a silicon dioxide, silicon nitride, polytetrafluoroethylene, or other insulating dielectric layer. Such strips can be separated from each other by a spacing that is small enough to be capable of generating heat in the semiconductor substrate <NUM> in response to the displacement current provided by the non-zero frequency applied electric field. The exact spacing for such heat generation may depend on the type of material of the semiconductor substrate <NUM>, the type or amount of doping of the semiconductor substrate <NUM>, the type or thickness of the insulator, the applied amplitude and frequency of the non-zero frequency applied time-varying electric field.

Moreover, the two or more electrodes 104A-B need not be located on the same side of the semiconductor substrate <NUM>. In an example, at least one of the two or more electrodes 104A-B can be located on an opposing side of the semiconductor substrate <NUM> from at least one other of the two or more electrodes 104A-B. For example, the two or more electrodes 104A-B can be located on the same side of the semiconductor substrate, with a further electrode <NUM> on the opposite side of the semiconductor substrate <NUM>, such as can be wider, e.g., to form a ground plane. Such an approach can be useful, for example, in a balanced line excitation approach, with V+ and V- applied to the two signal traces on the same side of the semiconductor substrate <NUM>, with respect to a ground plane, such as can be electrically connected to a ground or other reference voltage, on an opposing side of the semiconductor substrate <NUM>.

Additionally or alternatively, the two or more electrodes 104A-B can have a tapered or variable spacing from each other, rather than the fixed spacing shown in the parallel example of <FIG>. For example, the electrodes 104A-B can include segments that are separated from each other, but arranged with respect to each other at a <NUM> degree or other angle, such as diverging to form a "V" but without touching each other. As explained herein, the frequency of the applied electrical signal can be adjusted to shift the location of one or more current paths between the electrodes, such as to a location at which the spacing between the electrodes provides a certain match to the frequency. In a non-tapered example (e.g., parallel electrodes with the same spacing therebetween at all locations on the electrodes), the frequency of the applied electrical signal can be adjusted to increase or decrease the amount of heat generated by the resulting current flowing between the electrodes.

In various examples, the length of the conductive segments of the electrodes 104A-B can extend completely across the semiconductor substrate <NUM>, or can extend for a fraction of that distance, such as until all of the non-zero frequency applied electric field signal is absorbed by the semiconductor substrate <NUM>.

The line impedance presented the at least two electrodes 104A-B and the semiconductor substrate <NUM> region therebetween (e.g., with or without a ground plane on the opposing side of the semiconductor substrate <NUM>) can be determined by calculation or measurement. An impedance matching circuit can be included between the electric field signal generator <NUM> and the electrodes 104A-B, such as to increase or maximize power transfer therebetween. The impedance matching circuit can include a narrow bandwidth or other impedance matching circuit that can be configured to match, e.g., at a specified frequency of the time-varying electric field signal generator <NUM>, the line impedance presented by the two or more electrodes and the output impedance of the electric field signal generator <NUM>. Such an approach can enable creation of a desired match without the need to adjust frequency. It can be especially useful when a fixed frequency source is the only available source.

<FIG> shows an example of the system <NUM> that can optionally include a passive or active heat extractor <NUM>. The heat extractor <NUM> can be coupled to one or more instances of the semiconductor substrate <NUM> (or one or more localized regions of the one or more instances of the semiconductor substrate <NUM>). The heat extractor <NUM> is one example of how to establish or optimize a thermal extraction energy pathway, such as to help extract heat from the semiconductor substrate <NUM>. The extracted thermal energy can be transferred elsewhere, such as to a target object or space. An example of a passive heat extractor <NUM> can include a heat sink. The heat sink can be selected to have good thermal conductivity, for example, higher thermal conductivity than that of the semiconductor substrate <NUM>. The heat sink can be integrated with the semiconductor substrate, for example, by including metal or other thermally conductive regions on or in the substrate. The heat sink can be configured with one or more heat dispersion structures, such as one or more of one or more cooling fins such as can permit radiation or convection of heat such as away from the semiconductor substrate <NUM> or toward a target object or space. The heat sink can be configured with one or more fluid channels, such as can allow liquid or other fluid flow or transport therein, such as in a partially or fully contained manner, such as in a fluid flow circuit. An active heat sink can include a fan, pump, or other active device, such as to encourage heat flow away from the semiconductor substrate <NUM>. In an example, the heat extractor <NUM> can be controlled by a signal provided by the control circuit <NUM>, such as based on information from the temperature sensor <NUM> about the temperature of the semiconductor substrate <NUM> or about the target object or area or about the heat extractor <NUM> itself, depending on the selected one or more locations of one or more instances of the temperature sensor <NUM>.

<FIG> shows an example, similar to <FIG>, including an optional biasing heater <NUM>, such as can be used to pre-heat the semiconductor substrate <NUM>, such as to a desired temperature, such as at or just below what can be referred to as an atomic thermal equilibrium (ATE) temperature. Without being bound by theory, at the ATE temperature, it may be easier for the applied non-zero electric field to excite the majority carriers in the semiconductor substrate into oscillation with the semiconductor substrate to efficiently generate further thermal energy. The biasing heater <NUM> can include an electric or gas-fueled heater, or a magnetic induction heater that can include a loop or electromagnet to create eddy currents in the semiconductor substrate <NUM> to pre-heat the semiconductor substrate <NUM> to ATE for then applying the non-zero frequency time-varying electric field for generating further thermal energy in the semiconductor substrate <NUM>.

The biasing heater <NUM> can be omitted, and the system <NUM> can be controlled by the temperature sensor <NUM> and the control circuit <NUM> to operate at or near such an ATE temperature. For example, the heat extractor <NUM> can include an active heat extractor that can be controlled (e.g., in a closed-loop negative feedback arrangement) such as to extract thermal energy from the semiconductor substrate <NUM> at a rate that maintains a temperature of the semiconductor substrate <NUM> or near an ATE temperature or other temperature at which further thermal energy can be efficiently or most efficiently generated from the semiconductor substrate <NUM>.

<FIG> shows an example of a method <NUM> of operating one or more of the systems, or portions thereof, such shown in <FIG>. At <NUM>, a temperature of the semiconductor substrate <NUM> (or object or space to be heated by the semiconductor substrate) can be measured. At <NUM>, the measured temperature can be compared to a specified expected ATE temperature of the semiconductor substrate <NUM>. If the measured temperature is not at or above the expected ATE temperature, then at <NUM>, the semiconductor substrate <NUM> can be heated, and the temperature can be re-measured at <NUM>. Otherwise, at <NUM>, if the measured temperature is at or above the ATE temperature, a non-zero frequency time-varying electric field can be applied to the semiconductor substrate <NUM>, such as by the local electrodes that are located on the semiconductor substrate <NUM>, such as separated therefrom by a dielectric layer. A frequency or amplitude of the non-zero frequency time-varying electric field can be controlled, such as to obtain a desired degree of majority-carrier oscillation induced harmonic vibration of the lattice of the semiconductor substrate, thereby generating thermal energy in the semiconductor substrate. At <NUM>, thermal energy can be actively or passively extracted from the semiconductor substrate, such as for heating a target object or space. In an example, such thermal energy extraction at <NUM> can include thermoelectric cooling of the semiconductor substrate <NUM>. At <NUM>, a temperature of the semiconductor substrate can be measured. If the measured temperature exceeds a target temperature, e.g., of the semiconductor substrate <NUM>, or of an object or space to be heated by the semiconductor substrate <NUM>, then at <NUM>, the semiconductor substrate <NUM>' (or the target object or space) can be cooled, such as by an thermoelectric cooling device that can be integrated into the semiconductor substrate <NUM>. Otherwise, at <NUM>, if the temperature of the semiconductor substrate <NUM> (or the target object or space) is not at the target temperature, then the non-zero frequency time-varying electric field application can continue at <NUM>. When a desired amount of heat has been extracted, or when a temperature of the target object or space has been increased to be at or above a target temperature, then the method of <NUM> can be paused or can terminate.

<FIG> shows an example of a method <NUM> of operating of operating one or more of the systems, or portions thereof, such shown in <FIG> and <FIG>. At <NUM>, an electromagnetic signal generator <NUM> can output a time-varying signal of amplitude A and frequency F, which can be capacitively applied to the semiconductor substrate <NUM>, such as explained elsewhere in this document. At <NUM>, a temperature T of the substrate <NUM>, such as can be measured by the temperature sensor <NUM>, can be provided to the control circuit <NUM>, which at <NUM> can compare the measured temperature T to a desired or reference temperature Treff. If the measured temperature T is less than the reference temperature Treff, then process flow can proceed to <NUM>. If the measured temperature T is greater than the reference temperature Treff, then process flow can proceed to <NUM>. If the measured temperature T is equal to the reference temperature Treff, then process flow can return to <NUM>. Hysteresis can be used in the comparison, if desired.

At <NUM> (Treff > T), the frequency F can be increased by a specified incremental amount df. Then, at <NUM>, the frequency F can be compared to a maximum frequency limit Fmax. At <NUM>, if the incremented frequency F does not exceed F max, then process flow can return to <NUM>. Otherwise, if the incremented frequency F exceeds Fmax, then the frequency F can be limited at Fmax and process flow can continue to <NUM>, and amplitude A can be increased by an incremental amount da, before the process flow returns to <NUM>. A maximum permissible amplitude limit can be used, similar to the maximum frequency limit described.

In an example, the control circuit <NUM> (or other control device) can control the temperature, such as by establishing or adjusting Treff, such as to a specified fixed or variable value such as depending on the need for heat generation.

Although the present patent application has focused on using a semiconductor substrate, to which a time-varying electrical signal can be capacitively applied to generate heat in the semiconductor substrate, the present subject matter is not so limited. Instead of (or in addition to) the semiconductor substrate, a metal substrate material (or any other material that can provide free charged particles) can be used, with a time-varying electrical signal capacitively coupled thereto. The capacitive contacts can isolate the substrate. The associated dielectric isolation between the input signal and the substrate can inhibit or prevent a short-circuit through the substrate or other similar effects. Such dielectric isolation can also help enable use of the present techniques in applications such as in which a fire or other consequence of an electrical current short-circuit may be of concern.

One structure suitable for capacitively applying a time-varying electrical signal to a semiconductor or other substrate with electrical charged particle carriers that are free to move within the substrate, can include a pair of parallel linear signal traces, each of length L in a direction y, and separated from each other by a separation distance s, and isolated from a first side of the substrate by a dielectric layer of thickness t, with a conductive ground plane on the opposing second side of the substrate. For such a structure, the line impedance (with or without the ground plane) can be determined by calculation and confirmed by measurement. An example of appropriate calculations is described below.

For a substrate without a ground plane, using a conformal transformation and the Schwartz-Christofel transformation, it can be shown that the capacitance and conductance of an infinitely thick substrate for the parallel trace structure can be given by the equations below, neglecting the skin effect. In Equation <NUM>, Ci=the capacitance in air per unit length. In Equation <NUM>, C<NUM>=the capacitance of the electrodes due to the substrate, per unit length. In Equation <NUM>, these capacitances C<NUM> and C<NUM> add to give the total capacitance, per unit length. G=the conductance of the parallel trace structure, per unit length. <MAT> <MAT> <MAT>.

The substrate permittivity is given as <MAT>.

However, this expression may be complex due to its conductivity <MAT>.

In this case, the substrate permittivity becomes <MAT> where ω is the angular frequency 2πf and f is the frequency of operation. Then, the expressions for C<NUM> and Ctotal become complex and the imaginary term is G, the conductance per unit length. If the operating frequency f is zero, then the conductance G becomes <MAT>.

In Siemens per unit length. Also, note that if the substrate is absent, then <MAT>.

The effective relative permittivity is the ratio of the capacitance of the structure with the substrate to the capacitance without the substrate, e.g., the capacitance in free space. The time-varying frequency guided by the electrodes will have a wave velocity given by the ratio of c (the velocity of light in free space) and the square root of the effective relative permittivity, that is: <MAT> provided that the substrate is non-magnetic, with a permeability of µo. Thus, the effective relative permittivity becomes <MAT>.

The time-varying electromagnetic wave will propagate supported by the electrodes and the substrate as: <MAT> in the y-direction, where <MAT>.

If the wave propagation is lossless, when εr is real, then γ=jβ, where β is in radians/meter, and the electromagnetic wave propagates along the electrodes as: <MAT> where <MAT> is the velocity of light in free space. If C<NUM> is complex, then εreff is complex, γ = α + jβ, and the attenuation term α is the real part in amperes/meter. It becomes possible to design the structure so that all of the time-varying electromagnetic power on the electrodes has dissipated into the semiconductor substrate by the time that it has traversed the electrode length L and reached the end. The line impedance becomes: <MAT>.

When εreff is complex, then the line impedance is also complex. Matching into the electrodes is possible with a careful design of the matching structure, such as can include using Eq. <NUM>.

When the semiconductor substrate is of a finite thickness h, the equations can be slightly modified. The air capacitance term is identical to that previously presented. However, the substrate capacitance C<NUM> is now changed to: <MAT> where <MAT>.

Thus, the effective relative permittivity becomes: <MAT>.

The propagation constant γ in radians/meter, of the electromagnetic wave along the electrodes is given as: <MAT>.

Where c is the velocity of light in free space. If Cs is complex, then γ has an attenuation term, which is the imaginary part. It becomes possible to design the structure so that all the time-varying electromagnetic power on the electrodes has dissipated into the substrate at its end.

The impedance of this line becomes <MAT>.

When εreff is complex, then the line impedance is also complex.

Matching into the electrodes is possible with a careful design of the matching structure, such as can include using Eq. <NUM>.

When a ground plane is used with the two parallel electrode structure, the two electrodes become coupled microstrip lines and the analytic expressions can be used. The capacitance Cp between the two strips, and the individual strip capacitances Cg to the ground plane can be determined. The coupled lines have even and odd modes, but in the excitation model, one of the electrodes can be grounded, in which case odd-even modes are not excited. <MAT> <MAT> <MAT> <MAT> <MAT> <MAT>.

When the substrate is air, it has a permitivitty of εo, then the above capacitance expressions become Cga and Cpa with εr omitted in Equations <NUM> and <NUM>. Then the expressions for the total air substratae capacitance Ca=Cga + Cpa and the total capacitance with the dielectric substrate present is Cd = Cg + Cp. Then the effective relative permittivity becomes: <MAT>.

The impedance of the line becomes: <MAT>.

When ∈reff is complex, then the line impedance is also complex. Matching into the electrodes is possible with a careful design of the matching structure, such as can include using Eq. <NUM>.

The equations explained above for the three example configurations can be used to relate spacing, inductance, and frequency for most configurations of the electrodes, such as for creating heat and, optionally, for establishing a temperature gradient. Such a temperature gradient can be established by varying the spacing between electrodes-at points on respective electrodes that are closer together, the substrate will become hotter than at points on respective electrodes that are farther apart. <FIG> show examples of electrodes having variable electrode spacing, s, between nearest points on the respective electrodes. <FIG> shows an example of a serpentine electrode configuration. <FIG> shows an example of a diverging linear electrode configuration.

In general, for the configurations shown in <FIG>, the temperature in the y direction will be a function of frequency, F, and separation, s, such as expressed in the following equation.

For each electrode geometry, one can calculate the maximum and minimum match frequencies corresponding to the maximum and minimum spacing. Each set of electrodes and substrate characteristics also has a triggering frequency for heat production. Frequencies below the triggering frequency do not produce heat, because there is insufficient energy transfer at such frequencies. An external impedance matching circuit can be added in series between the time-varying electric field signal generator circuit <NUM> and the capacitive electrodes 104A-B on the semiconductor substrate, such as to provide a desired impedance matching to permit heat production in the semiconductor substrate at a desired frequency.

As shown in Eq. <NUM>, temperature at any point y along the central axis is a function frequency (F) and spacing s. For any (frequency, spacing) combination, the temperature is maximum at location y where the match is complete or near complete. A gradient occurs on either side of y due to varying degrees of matching. By altering frequency one can effectively move the point of maximum heat generation, and by implication the gradient, up and down along the y axis. The flow chart shown in <FIG> describes an example of a process that can be used to control such a device, such as to establish a desired temperature gradient. The case of parallel electrodes is a special case in which spacing between the electrodes is constant, and thus the percentage of matching is the same along the entire electrode length, which does not permit a temperature gradient in this fashion in the absence of losses occurring along the length of the electrodes in the y-direction.

However, one can also create a temperature gradient by placing heat sinks or cooling cells at different locations on the substrate. Each cooling cell can be controlled separately or independently, such as by the control circuit <NUM> or by an external microprocessor based control system that can manage the heat output of each cell to establish and manage a temperature gradient.

For a heat production application with sufficient space and sufficiently coarse control, the length of the electrode can be adjusted such that all of the energy from the time-varying signal provided by the electric field signal generator <NUM> can be dissipated along the length of the electrode. A temperature gradient can be formed because the amount of energy transferred or left in the signal decreases as the signal traverses the length of the electrode. Further control on heat production can be exercised by adjusting the amplitude of the input signal, such as in cases in which a maximum frequency has been reached, as explained in <FIG>.

Preliminary laboratory experiments were conducted to test the viability of the present approach to time-varying frequency-controlled heat production in a semiconductor substrate.

A p-type <<NUM>> silicon semiconductor wafer substrate with resistivity in the <NUM>-<NUM> ohms/cm<NUM> range was used. A <NUM> Angstrom layer of silicon dioxide (SiO2) was grown on a top surface of the silicon wafer. Two parallel <NUM> centimeter long strips of copper metallization were formed upon the SiO2 on the silicon wafer as electrodes. The spacing between electrodes was <NUM> millimeters in this specimen.

A Signatone probe station was used. The specimen was placed on an insulated jig on the copper base plate of the probe station, to inhibit or prevent the base plate from acting as a heat sink. A frequency generator with a range of up to <NUM> was provided for connection to the electrodes in a quiet semi-dark room with a temperature controlled environment that was maintained at room temperature of <NUM> degrees Celsius. Any focused lamps were turned off after being used for establishing probe contacts with the specimen. For injecting the time-varying frequency signal onto the electrodes, an RF GGB Pico probe was used (GS configuration) to inhibit RF spatter. A <NUM> Watt amplifier was placed in series with the input signal probe. An RTD temperature sensor was used for measuring the semiconductor substrate temperature and another was left to monitor a reference room temperature measurement. Table <NUM>, below, shows the experimental results of the change of the temperature of the semiconductor substrate (for a single sample of the semiconductor substrate) as a function of change of frequency of the input signal. The duration between changes in input frequency was set to <NUM> minutes to help provide steady-state data for each frequency.

As a further verification that frequency was the only change to the overall all experimental setup affecting the temperature changes we randomly changed frequency up and down to the values shown in the table. Each time the temperature stabilized at the same value for the particular frequency.

In this document, the term "substrate" includes the active material layer that actively produces heat by the capacitively coupled non-zero frequency time-varying electric field applied thereto. Other types of material layers may be attached to the active layer or layers, such as for heat extraction or for one or more other application specific needs. The substrate can include a single type of semiconductor material or a composite material, which can include multiple types of semiconductor materials, one or more Peltier materials, or one or more other application-specific materials. A composite can be created, for example, by bonding one or more types of materials though one or more bonding processes such as, e.g., direct bonding, glue or adhesive, etc. In an example, a thin film metal material and a semiconductor material can be bonded together, and either or both can function as the active heat source, such as concurrently.

Ohmic contacts can be used to operate under similar principles as described herein for capacitive coupling, except without capacitive coupling the displacement current does not occur. Still, localized control of heat generation, such as by controlling the frequency of the applied electrical signal, is believed to be possible using ohmic contacts as well as using capacitive contacts. <FIG> shows several substrate examples. In <FIG>, capacitive electrodes 804A-B can be located upon a semiconductor, thin-film metal, or other substrate <NUM>, e.g., separated therefrom by an electrical insulator or dielectric layer 803A-B.

In <FIG>, the electrical insulator 803A-B can be omitted and the electrodes 804A-B can be located on the substrate <NUM>, such as Schottky diode contacts, which can include a semiconductor or thin-film metal substrate forming a Schottky diode connection with the electrodes 804A-B.

In <FIG>, the substrate can include a composite substrate <NUM>, such as can include multiple substrates 802A-B that can be bonded together to provide a combination of one or more substrate characteristics (e.g., lattice alignment, doping type or concentration or both, etc.) that are suitable for a particular application. For example, a semiconductor or thin-film metal substrate 802A, which can be bonded to a Peltier material substrate 802B, such as by an electrical insulator 803A-B. The electrical insulator 803A-B can be thermally conductive, e.g., using a bonding material having a specified thermal conductivity, which can be specified to be higher than the thermal conductivity of one or both of the substrates 802A-B. In an example, the Peltier material can include bismuth telluride.

In an example, one or both of the substrates 802A-B can be actively excited through a capacitively coupled non-zero frequency time-varying electric field, such as by a set of capacitive electrodes that can be shared between the substrates 802A-B (e.g., sandwiched between the substrates 802A-B) or separately dedicated to a respective individual substrate 802A (e.g., located upon faces of the substrates 802A-B that are opposite from an adjacent face between the substrates 802A-B).

<FIG> shows an example in which multiple electrodes 804A-B can be sandwiched between the substrates 802A-B without an electrical insulator intervening between the electrodes 804A-B and the respective substrates 802A-B, such as in an arrangement in which Schottky capacitive contacts are desired.

<FIG> shows an example in which multiple electrodes 804A-B can be sandwiched between the substrates 802A-B with a respective electrical insulator 803A-D intervening between the electrodes 804A-B and the respective substrates 802A-B, such as in an arrangement in which non-Schottky capacitive contacts are desired.

<FIG> shows an example in which electrodes 804A-B are separated from a thin-film metal substrate 802A by an insulator 803A-B, such as with the thin-film metal substrate 802A being deposited or otherwise formed upon an underlying supporting substrate 802B, which, in an example, can include a heat sink material having greater thermal conductivity than the thin-film metal substrate 802A and lower electrical conductivity than the thin-film metal substrate 802A. In an example, the heat sink material of the supporting substrate 802A can include diamond or an intrinsic or lightly-doped semiconductor material.

The above description includes references to the accompanying drawings, which form a part of the detailed description. These embodiments are also referred to herein as "aspects" or "examples.

In the event of inconsistent usages between this document and any documents cited, the usage in this document controls.

Geometric terms, such as "parallel", "perpendicular", "round", or "square", are not intended to require absolute mathematical precision, unless the context indicates otherwise. Instead, such geometric terms allow for variations due to manufacturing or equivalent functions. For example, if an element is described as "round" or "generally round," a component that is not precisely circular (e.g., one that is slightly oblong or is a many-sided polygon) is still encompassed by this description.

Claim 1:
An apparatus comprising:
a substrate (<NUM>); and
two or more electrodes (104A, 104B), formed directly or indirectly on the substrate (<NUM>), the electrodes (104A, 104B) including first and second electrodes separated from each other by different minimum spacing at different locations along a length of at least one of the first and second electrodes (104A, 104B),
wherein the electrodes (104A, 104B) are configured to receive a non-zero frequency time-varying electrical energy that is coupled by the electrodes (104A, 104B) to the substrate (<NUM>) to trigger a current to generate a frequency-controlled heat source in the substrate (<NUM>), and wherein a location of the heat source is selected along the length of the electrodes (104A, 104B) by adjusting the frequency of the time-varying electrical energy,
thereby providing at least one corresponding frequency-dependent current path between the first and second electrodes (104A, 104B) to provide the frequency-controlled heat at the heat source location in the substrate (<NUM>).