Method of operating a piezoelectric plasma generator

Abstract

A method of operating a piezoelectric plasma generator (14) comprising applying an input signal (S in ) to a piezoelectric transformer (1) of the piezoelectric plasma generator (14), wherein an absolute value (|A peak |) of a peak amplitude of the input signal (S in ) is periodically reduced and increased to a level less than and greater than a strike voltage (V ig ) of the plasma generator (14) such that a plasma periodically collapses.

Description

[0001] The present invention relates to a method of operating a piezoelectric plasma generator. In particular, the plasma generator generates a non-thermal plasma. The plasma can be generated under atmospheric conditions. The plasma generator can be used for treating sensitive surfaces, for example such as thin fabrics or skin.

[0002] Patent application DE 10 2017 105 415 A1 discloses a piezoelectric plasma generator for generating a non-thermal plasma, wherein the input signal is optimized such that the field strength at the transformer output region is maximized. Patent application DE 10 2015 119 574 A1 discloses a method for generating a non-thermal plasma, wherein the control circuit comprises an inductance and wherein the average current is measured to control the input frequency of the transformer. Patent application DE 10 2015 112 410 A2 discloses a method of operating a piezoelectric plasma generator, wherein phase information of the input impedance is determined and the frequency of the input signal is controlled depending on the phase information.

[0003] DE 10 2017 105 401 A1 discloses a piezoelectric plasma generator, wherein the input voltage is modulated such that, in addition to generating a plasma, an ultrasonic signal is generated.

[0004] Patent application WO 2015 / 083155 A1 discloses a radio frequency (RF) plasma generator, wherein a non-thermal plasma is generated by a radio frequency (RF) electromagnetic (EM) field. In order to prevent unwanted arcing, the RF power source can be switched off for a short time during operation.

[0005] DE 10 2016 110 141 A1 discloses a method for operating an HF plasma generator, wherein the input voltage is periodically lowered to a level at which the plasma discharge is maintained. EP 3 662 854 A1 discloses a method for operating an HF plasma generator, wherein the input voltage is dynamically adapted in order to maintain the plasma and at the same time to minimize unwanted side effects such as light and noise generation. DE 19 616 187 A1 discloses a method for operating a transformer for generating a plasma, wherein short voltage pulses are applied to the input voltage.

[0006] It is an object of the present invention to provide an improved method of operating a piezoelectric plasma generator.

[0007] In one aspect, the present invention relates to a method of operating a piezoelectric plasma generator. Such a piezoelectric plasma generator comprises a piezoelectric transformer comprising an input side and an output side. An input signal, i.e. an input voltage, is applied to the input side. Due to the piezoelectric effect, a high output voltage can be generated at one end of the output side.

[0008] The input signal can be based on a base signal having a first frequency. For example, the signal shape of the base signal can be sinusoidal. The base signal can have a constant first frequency. The first frequency can correspond to a resonance frequency of the piezoelectric transformer. For example, the resonance frequency can be approximately 50 kHz. By "corresponding" it is meant that the first frequency is close to or equal to the resonance frequency. When the plasma generator is operated at its resonance frequency, the efficiency of the plasma generation is optimized.

[0009] The base signal can be modulated by a modulation signal having a second frequency that is smaller than the first frequency.

[0010] The input signal is such that the absolute value of the peak amplitude of the input signal periodically decreases and increases to a level that is smaller and larger than the ignition voltage of the plasma generator. The level that is smaller than the ignition voltage causes the plasma generation to collapse. Thus, the lower level is not sufficient to maintain the plasma generation. Therefore, the base signal can be bounded by an envelope curve. The length of time during one oscillation period of the peak amplitude in which the absolute value of the peak amplitude is larger than the ignition voltage is the "on-time", and the length of time during one oscillation period of the peak amplitude in which the absolute value of the peak amplitude is smaller than the ignition voltage is the "off-time".

[0011] The field strength on the output of the piezoelectric transformer that is required to generate the plasma is the ignition field strength. The input voltage that is required to generate the ignition field strength is the ignition voltage.

[0012] By periodically lowering the absolute value of the peak input voltage below the ignition voltage, there is an effect that the average energy input into the substrate can be reduced. In addition to this, the occurrence of so-called streamers can be prevented or reduced. When these streamers hit the surface of a sensitive substrate, such as a thin fabric or skin, local burn marks can occur. Thus, the sensitive substrate can be damaged, which is an undesirable effect. Furthermore, the thermal power can cause an excessive increase in temperature in the substrate, which can damage the substrate.

[0013] Controlling the occurrence of streamers and the average energy input is particularly important when the plasma treatment is of electronic components that are very sensitive to electrostatic discharge. For example, the plasma treatment can comprise cleaning and / or activating a surface. Furthermore, the activation of delicate and sensitive structures, such as thin insulating polymer foils or conductive metal tracks, is possible when the average energy input is reduced.

[0014] A further example for operation is a substrate which is difficult to activate, e.g. a metal / conductive surface such as carbon black plastic material. When there is a high current, the surface cannot be activated on a large scale and there is no temperature increase. This can be due to the plasma cloud reducing in its volume - due to the lower potential of the substrate. When the input signal is provided periodically below the ignition voltage, the current is interrupted and a large-scale activation without temperature increase is possible.

[0015] A further example is operation in an environment with low heat dissipation, e.g. in a vacuum. In this case, the self-heating of the plasma generator cannot be dissipated and the reliability of the plasma generator is reduced. When the absolute value of the peak voltage is reduced periodically below the ignition voltage, the internal temperature can be reduced while the plasma generation during the on-cycle can be maintained at the same level.

[0016] A further example for operation is operation with a medium which requires a high ionization voltage, such as N2, SF6. For such media, the reliability of the plasma generator is usually reduced due to self-heating at high power input. By periodically switching off and on the base voltage and selecting a suitable duty cycle, the self-heating can be reduced. Thus, the reliability can be increased.

[0017] The modulation signal can be a modulation function which scales the base signal. For example, the modulation signal can have values between 1 and 0.

[0018] The modulation signal can be pulse-shaped. In particular, the modulation signal can periodically switch between a high level and a low level.

[0019] The high level can be 1. In this case, the modulation signal can correspond to the base signal during the high level time. The low level can be zero. In this case, the input voltage is switched to zero during the low level time.

[0020] In a further embodiment, the low level can be above zero. As an example, the high level can be 1.0 and the low level can be 0.5. In this case, oscillations of the components can be maintained and mechanical stress on the components can be reduced.

[0021] In a further embodiment, the modulation signal can be a continuous oscillation signal, e.g. such as a sinusoidal signal. In this case, the input signal is also continuously oscillating, which reduces mechanical stress on the components. In particular, the modulation signal can have the shape of a sinusoidal signal absolute value.

[0022] According to embodiments, the duty cycle of the input signal can be adjusted during operation of the plasma generator. The duty cycle is the proportion of one oscillation period of the absolute value of the peak amplitude and one oscillation period of the absolute value of the peak amplitude during which the absolute value of the peak amplitude is greater than the ignition voltage "on time". One oscillation period of the absolute value of the peak amplitude can correspond to one oscillation period of the modulation signal.

[0023] In all embodiments, the absolute value of the peak amplitude during the off time, in which the absolute value of the peak amplitude is less than the ignition voltage, can be above zero at least for most of the off time. Thus, the oscillation of the piezoelectric transformer can be maintained during the off time. In particular, the peak amplitude during the off time can be such that the oscillation is maintained during the entire off time between the on times. This has the advantage that the transition between plasma generation and collapse of the plasma generation is smoother and the mechanical stress imposed on the transformer is less.

[0024] The average energy emitted from the plasma generator depends on the duty cycle and the frequency of the modulation signal. When the duty cycle is high, the average emission energy is high. When the duty cycle is low, the average emission energy is low.

[0025] Adjusting the duty cycle can be done almost steplessly and enables fine-tuning of the energy input. This is particularly important for sensitive substrates or for cosmetic and medical applications. The duty cycle can be adjusted while the frequency of the modulation signal remains at a fixed value.

[0026] According to embodiments, the duration of the off time, in which the peak amplitude is below the ignition voltage, is at most 10 ms or at most 5 ms. By periodically reducing the absolute value of the peak amplitude, the ignition channel, i.e. the path of the ionized gas extending from the transformer output side, is forced to break down again and again.

[0027] After reducing the absolute value of the peak amplitude, the high output voltage decays. When the output voltage falls below the ignition voltage, the current in the ignition channel collapses. However, the higher concentration of charge carriers in this region is maintained for a short time span. When the base signal switches on again during this time span, a new ignition of the plasma is significantly easier and takes place at a lower voltage. Due to the lower ignition voltage, the mechanical stress on the components is reduced, which leads to higher reliability.

[0028] According to embodiments, the second frequency, i.e. the frequency of the modulation signal, is at most 1 / 20 of the first frequency, i.e. the frequency of the base signal. This can ensure that the plasma generation is stopped even at a given inertia of the piezoelectric transformer.

[0029] After the off-time in which the absolute value of the peak amplitude is smaller than the ignition voltage, the first frequency, i.e. the frequency of the base signal, can be adjusted to the resonance frequency of the plasma generator. For this purpose, a parameter corresponding to the offset of the first frequency from the resonance frequency can be obtained and the frequency of the base signal is readjusted so that it corresponds to the resonance frequency.

[0030] This enables an optimal mode of operation under varying loads, e.g. due to varying substrate properties, gas mixtures, materials or working distances.

[0031] According to a further aspect, a piezoelectric plasma generator comprising a piezoelectric transformer is disclosed. The plasma generator comprises a control circuit for providing an input signal to the piezoelectric transformer. The control circuit can be configured for operating the plasma generator according to the method described in the foregoing.

[0032] The control circuit can comprise a base signal generator for generating a base signal having a first frequency and a modulation signal generator for generating a modulation signal having a second frequency lower than the first frequency. The control circuit can further comprise a signal mixer for mixing the base signal with the modulation signal so that the input signal is provided, wherein the absolute value of the peak amplitude of the input signal is periodically reduced and increased to a level smaller and larger than an ignition voltage of the plasma generator.

[0033] The control circuit can further comprise a measurement device for measuring a parameter related to the energy input provided by the plasma generator to a substrate of a plasma process, wherein the modulation signal is adjusted depending on the measured energy input.

[0034] The control circuit can be configured to adjust a duty cycle during operation, the duty cycle being the proportion of an on-time in which the absolute value of the peak amplitude is larger than the ignition voltage in one oscillation period of the absolute value of the peak amplitude.

[0035] The control circuit can further comprise a measurement device for measuring a parameter related to the offset of the first frequency from a resonance frequency of the plasma generator. The measurement device can be the same measurement device for measuring the energy input in the substrate or can be a further measurement device. Suitable measurement devices are disclosed in the beginning of the cited patent application.

[0036] Depending on the measured offset, the control circuit can be configured to readjust the first frequency to correspond to the resonance frequency.

[0037] The present disclosure comprises several aspects of the invention. Each feature described with respect to one aspect is also disclosed herein with respect to another aspect, even if the respective feature is not explicitly mentioned in the context of a particular aspect.

[0038] Further features, refinements and expedients become clear from the following description of exemplary embodiments in connection with the figures.

[0039] Figure 1 Fig. 1 shows a schematic illustration of a piezoelectric transformer for a piezoelectric plasma generator,

[0040] Figure 2A 2B Fig. 2C, 2D show examples of different base signals,

[0041] Figure 3A 3B Fig. 3C shows an example of a different modulation signal,

[0042] Figure 4 Fig. 4 shows input signals for operating the piezoelectric transformer according to a first embodiment,

[0043] Fig. 5 shows a further example of a modulation signal,

[0044] Figure 6 Fig. 6 shows input signals for operating the piezoelectric transformer according to a further embodiment,

[0045] Figure 7 Fig. 7 shows a further example of a modulation signal,

[0046] Figure 8 Fig. 8 shows input signals for operating the piezoelectric transformer according to a further embodiment,

[0047] Figure 9 Fig. 9 shows a schematic circuit diagram of a piezoelectric plasma generator according to an embodiment.

[0048] In the figures, elements of identical structure and / or functionality can be referred to by identical reference signs. It is understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0049] Figure 1 Fig. 1 shows a piezoelectric transformer 1 in a perspective view. The piezoelectric transformer 1 can be used in a plasma generator for generating a plasma, in particular a non-thermal low-pressure plasma or an atmospheric pressure plasma or a high-pressure plasma. The piezoelectric transformer 1 is an embodiment of a resonant transformer which is based on piezoelectricity and, in contrast to conventional magnetic transformers, forms an electromechanical system. For example, the piezoelectric transformer 1 is a Rosen-type transformer. Alternatively, other types of piezoelectric transformers can be used.

[0050] ​​The piezoelectric transformer 1 has a first region 2 as an input region and a second region 3 as an output region, wherein a direction from the first region 2 to the second region 3 defines a longitudinal direction z. The first region 2 comprises an input-side end region 4 and the second region 3 comprises an output-side end region 5.

[0051] In the first region 2, the piezoelectric transformer 1 comprises internal electrodes 6, 7 to which an alternating voltage can be applied. The internal electrodes 6, 7 extend in the longitudinal direction z of the piezoelectric transformer 1. The internal electrodes 6, 7 are alternately stacked with piezoelectric material 8 in a stacking direction x perpendicular to the longitudinal direction z. The piezoelectric material 8 is polarized in the stacking direction x.

[0052] The internal electrodes 6, 7 are arranged inside the piezoelectric transformer 1 between layers of piezoelectric material 8 and are also referred to as internal electrodes. The piezoelectric transformer 1 comprises a first side surface 9 and a second side surface 10 opposite the first side surface 9. On the first and second side surfaces 9, 10, external electrodes 11, 12 are arranged. The internal electrodes 6, 7 are alternately connected to one of the external electrodes 11, 12.

[0053] The second region 3 comprises piezoelectric material 13 and is free of internal electrodes. The piezoelectric material 13 in the second region 3 is polarized in the longitudinal direction z. The piezoelectric material 13 of the second region 3 can be the same material as the piezoelectric material 8 of the first region 2.

[0054] The piezoelectric materials 8 and 13 differ in their respective polarization direction. In particular, in the second region 3, the piezoelectric material 13 is formed as a single monolithic layer which is completely polarized in the longitudinal direction z. Thus, the piezoelectric material 13 in the second region 3 has only one single polarization direction.

[0055] Via the external electrodes 11, 12, a low alternating voltage can be applied between adjacent internal electrodes 6, 7 in the first region 2. Due to the piezoelectric effect of the piezoelectric material 8, the alternating voltage applied on the input side is converted into mechanical oscillations. Thus, when an alternating voltage is applied to an electrode 6 in the first region 2, a mechanical wave is formed within the piezoelectric material 8, 13 which generates an output voltage in the second region 3 by means of the piezoelectric effect.

[0056] Between the output-side end region 5 and the ends of the electrodes 6, 7 of the first region 2, a high voltage is generated. This also creates a high potential difference between the output-side end region 5 and the surrounding environment of the piezoelectric transformer 1, which is sufficient to generate a strong electric field which ionizes the surrounding medium and causes the generation of a plasma. The field strength required for the ionization of atoms or molecules or the generation of free radicals, excited molecules or atoms in the surrounding medium is referred to as the ignition field strength of the plasma. If the electric field strength on the surface of the piezoelectric transformer 1 exceeds the ignition field strength of the plasma, ionization occurs. In the following, the voltage at which the ignition field strength is achieved is referred to as the ignition voltage.

[0057] The piezoelectric transformer 1 can be used to generate plasma in a variety of applications. In particular, the piezoelectric transformer 1 can be used for plasma treatment of surfaces. The surface can be a part of the human body, such as a finger. Alternatively, the object being treated can be any object having a surface including, for example, materials that will be cleaned and / or modified by plasma treatment. In particular, the piezoelectric transformer 1 can be part of a handheld device that does not need to be placed inside a gas chamber along with the object being treated.

[0058] Figure 2A , 2B 2C and 2D show different fundamental signals S base That is, the basic signal shape of the voltage U provided to the external electrodes 11 and 12 for generating plasma as a function of time t.

[0059] Basic signal S base frequency f base This can correspond to the resonant frequency of a piezoelectric transformer. The resonant frequency depends not only on internal factors of the transformer, such as its geometry, but also on external factors, such as the load established by the interaction of ignited plasma with the substrate. Furthermore, the resonant frequency can also depend on, for example, the temperature of the transformer.

[0060] The control circuit can record the offset between current and voltage and modify the fundamental signal so that the current and voltage exhibit a phase shift close to 0°. Alternatively or additionally, the field strength in the output region can be measured using a field probe, and the frequency of the input signal can be adjusted to achieve the maximum field strength. In this case, the fundamental signal S base The frequency corresponds to the resonant frequency.

[0061] The resonant frequency can be below 100 kHz. As an example, the resonant frequency can be no higher than 99 kHz. The resonant frequency can be at least 10 kHz. For example, the resonant frequency can be in the range of 10 kHz to 90 kHz. In a particular embodiment, the resonant frequency can be approximately 50 kHz.

[0062] Basic signal S base It can have, for example Figure 2A The serrated shape shown is as follows: Figure 2B The rectangular shape shown, such as Figure 2C The triangle shape shown or as Figure 2D The sinusoidal shape shown. Other shapes are based on the signal S. base That's also possible.

[0063] The input voltage can range from a few volts, while the output voltage at the transformer tip can range from several kilovolts. As an example, the peak-to-peak input voltage U...pp - is the distance A between the positive and negative peak amplitudes peak - can be in the range of 12 to 24 V and the output voltage can be up to e.g. 30 kV. The absolute value of the peak amplitude |A peak is at a constant level.

[0064] During transformer operation, so-called streamers can occur at the corners of the output side end region in the ignition plasma region. When these streamers hit the surface of a sensitive substrate such as a thin fabric or skin, local burn marks can occur. Thus, the sensitive substrate can be damaged, which is an undesirable effect. Furthermore, the thermal power can lead to an excessive increase in temperature in the substrate, which can damage the substrate.

[0065] In order to avoid local high temperatures caused by such streamers, the peak amplitude A peak of the input signal supplied to the transformer can be periodically reduced and increased to a level smaller and larger than the ignition voltage of the plasma generator. The reduction of the absolute value of the peak amplitude A peak has the effect of a reduced high local power density which leads to damage. In particular, a leakage current can be achieved, which also meets the DIN specification DIN EN 60601-1 [3].

[0066] By modulating the base signal, e.g. one of the base signals S base shown in Fig. Figures 2A-2D , with a modulation signal, a resulting modulated input signal can be achieved.

[0067] Figure 3A , 3B and 3C show different embodiments of a modulation signal S mod with a pulse shape. The pulse signal shapes differ in their duty cycle DC. The duty cycle DC is the proportion of the "on time" T on , wherein for the resulting modulated input signal the absolute value of the peak amplitude is greater than the ignition voltage for one oscillation period of the peak amplitude. The pulse signal shapes oscillate between the levels 1 and 0. The length of the pulses at level 1 corresponds to the "on time", the time between such pulses corresponds to the "off time".

[0068] The frequency of the modulation signal S mod is smaller than the frequency of the base signal S base . The maximum frequency of the modulation signal can be 1 / 20 of the plasma generator resonance frequency. Thus, for a resonance frequency in the range of 10 kHz to 100 kHz, the maximum frequency of the modulation signal S mod is between 0.5 kHz and 5 kHz.

[0069] In order to dynamically adjust the base signal Sbase The frequency of the modulation signal S is such that it approaches the resonant frequency of the plasma generator, and the duty cycle DC must be large enough to obtain a sufficient number of fundamental signal cycles. mod At a frequency of 0.5 kHz, the duty cycle DC can be at least 0.5%, and at a frequency of 5 kHz, at least 5%. In this case, there is a fundamental signal S with a frequency of 50 kHz in each duty cycle DC. base At least ten complete cycles.

[0070] exist Figure 3A In the middle, the modulation signal S mod With a 20% duty cycle DC, in Figure 3B In the middle, the modulation signal S mod With a 50% duty cycle, and in Figure 3C, the modulation signal S mod It has an 80% duty cycle. For example, it can be modulated by such a pulse signal S through a periodically closing and opening switch. mod To modulate the fundamental signal S base As an example, transistors can be used to switch voltages.

[0071] Figure 4 It shows the basic signal S base The generated input signal S in Basic signal S base Having such Figure 2D The sinusoidal shape shown is based on the modulation signal S shown in Figure 3C. mod It is periodically switched on and off. Therefore, the absolute value of the peak amplitude |A peak | Switches between the absolute value and zero value of the peak amplitude of the basic signal.

[0072] For example, by using the fundamental signal S base With modulation signal S mod The modulation signal S is calculated by multiplication. mod Phase shifting can be applied to ensure the modulation signal S mod It always starts increasing from zero voltage.

[0073] In order to achieve the shutdown time T off Afterwards, plasma ignition is easier, and the turn-off time T off It should not be too long. As an example, a suitable duration for the shutdown time is 10 ms or less. In some embodiments, 5 ms may be the upper limit for the shutdown time.

[0074] The plasma generator can be operated such that the duty cycle DC is adjusted so that a desired amount of energy input to the substrate can be achieved. Such adjustment can be done dynamically during operation so that the duty cycle varies during operation.

[0075] The average energy emitted from the plasma generator depends on the duty cycle and the frequency of the modulation signal S mod . When the duty cycle is high, the emitted energy is high. When the duty cycle is low, the emitted energy is low.

[0076] Adjusting the duty cycle enables control of maximum energy transfer and maximum patient leakage current, for example, without changing the geometric distance, adding additional dielectric barriers, and / or changing the process medium.

[0077] According to an embodiment, a parameter corresponding to the energy input in the substrate or substrate surface is determined. Depending on the determined value, the duty cycle can be adjusted so that the average energy increases or decreases over time.

[0078] When the base signal is switched on again, the frequency f base of the base signal S base may be readjusted to the resonance frequency. For this purpose, a parameter corresponding to the offset of the frequency from the resonance frequency can be obtained, and the frequency of the base signal is readjusted so that it corresponds to the resonance frequency. Such readjustment can be done in each cycle when the base signal is switched on again. When the frequency of the modulation signal is 5 kHz, the readjustment is accordingly done once every 200 cycles.

[0079] Fig. 5 shows a further embodiment of the pulse-shaped modulation signal S mod . In this embodiment, the modulation signal S mod oscillates between the levels 1 and 0.5.

[0080] Figure 6 shows the resulting input signal S mod obtained from the modulation of the sinusoidal base signal S base by the modulation signal S in of Fig. 5. During the off-time T off , the absolute value of the peak amplitude |A peak | is not zero, but half the amplitude of the absolute value |A on | during the on-time T peak . During the off-time T off , the absolute value of the peak amplitude |A peak | is smaller than the ignition voltage V ig , and the plasma generation stops.

[0081] Fig. 6 shows a further embodiment of the pulse-shaped modulation signal S modOther levels are possible. However, the low level should be low enough that the input voltage is below the ignition voltage and the plasma collapses. A sufficiently high low level can be chosen to maintain component oscillation so that the next ignition begins at a lower ignition voltage, achievable with only a slight increase in the input voltage. Such a "hot" restart reduces mechanical stress on the component and significantly increases reliability.

[0082] Such modulation has the advantage of supporting the oscillating motion of the piezoelectric transformer between high pulses.

[0083] Figure 7 The modulation signal S is shown mod Another example is where the signal oscillates continuously, unlike... Figure 3A Switching between 3C and the fixed level shown in Figure 5. Modulation signal S mod It has a shape with the absolute value of a sinusoidal oscillation. The continuous oscillation shown is suitable for maintaining the continuous oscillation of a piezoelectric transformer.

[0084] Figure 8 The input signal S is shown. in In the embodiment, the absolute value of the peak amplitude |A peak Continuous oscillation. Input signal S in Based on Figure 7 The modulation signal S shown mod Modulated sinusoidal fundamental signal. Peak amplitude |A peak | The route follows a modulated signal S mod The shape of the envelope curve.

[0085] The resulting amplitude-modulated input signal S in The duty cycle DC here is also called the "on time" T. on The input signal S in The absolute value of the peak amplitude |A peak The time T is greater than the ignition voltage and generates plasma, and the length of the entire oscillation cycle of the peak amplitude absolute value—that is, the "on-time". on and "shutdown time" T off The sum of these values ​​is related, where the absolute value of the peak voltage is less than the ignition voltage V. ig .

[0086] Similarly, in this embodiment, the peak amplitude |A| during the off-time is... peak This allows plasma generation to collapse during the off-time, but simultaneously, the oscillation of the piezoelectric transformer is maintained during the off-time. Peak amplitude |A peak The input voltage U(t) is above zero for most of the off-time. Specifically, the input voltage U(t) has several oscillation periods during the off-time, with the peak amplitude |A| exceeding zero in most of these periods.peak | is close to zero only during a single period of the off-time. peak | is close to zero only during a single period of the off-time.

[0087] Figure 9 A piezoelectric plasma generator 14 is shown, which comprises a control circuit 15 and a piezoelectric transformer 1.

[0088] The control circuit 15 comprises a base signal generator 16, which supplies a base signal, for example one of the base signals shown in Fig. 1. The control circuit 15 further comprises a modulation signal generator 17, in which a modulation signal is defined, and a signal mixer 18, which mixes, for example scales, the base signal with the modulation signal, so that a modulated input signal is generated. Figures 2A-2D

[0089] The control circuit 15 further comprises a measurement device 19 for determining a parameter of the plasma generator 14 during operation. The measurement device 19 can determine the shift of the resonance frequency from the base signal frequency. The measurement device 19 can alternatively or additionally determine the energy and / or the current input into the substrate.

[0090] The measurement of the measurement device can be provided to the base signal generator 16, so that the frequency of the base signal can be periodically adjusted to the resonance frequency.

[0091] Furthermore, the measurement of the measurement device 19 can be provided to the modulation signal generator 17. The modulation signal generator 17 can adjust the duty cycle of the modulation signal in order to dynamically reduce or increase the energy or the current input into the substrate.

[0092] In some embodiments, the input signal can be switched off completely depending on the measurement. As an example, the input signal can be switched off when the energy input into the substrate is too high and / or too low.

[0093] Reference signs

[0094] 1 piezoelectric transformer

[0095] 2 first region

[0096] 3 second region

[0097] 4 input-side end region

[0098] 5 output-side end region

[0099] 6 first inner electrode

[0100] 7 second inner electrode

[0101] 8 piezoelectric material ​

[0102] 9 first side surface

[0103] 10 second side surface

[0104] 11 first external electrode

[0105] 12 second external electrode

[0106] 13 piezoelectric material

[0107] 14 piezoelectric plasma generator

[0108] 15 control circuit

[0109] 16 base signal generator

[0110] 17 modulated signal generator

[0111] 18 signal mixer

[0112] 19 measuring device

[0113] 20 substrate

[0114] z longitudinal direction

[0115] x stacking direction

[0116] S in input signal

[0117] S base base signal

[0118] S mod modulated signal

[0119] f base base signal frequency (first frequency)

[0120] f mod modulated signal frequency (second frequency)

[0121] A peak peak amplitude

[0122] |A peak | absolute value of the peak amplitude

[0123] U pp peak-to-peak voltage

[0124] V ig ignition voltage

[0125] T on turn-on time

[0126] T off turn-off time

[0127] T cycle Cycle time

[0128] DC duty cycle.

Claims

1. A method for operating a piezoelectric plasma generator, This includes applying an input signal (S) to the piezoelectric transformer (1) of the piezoelectric plasma generator (14). in The steps, The input signal (S) in The absolute value of the peak amplitude (|A) peak |) Periodically decrease and increase the ignition voltage (V) of the plasma generator (14) to be less than and greater than the ignition voltage (V) of the plasma generator (14). ig The level of this phenomenon causes the plasma to collapse periodically during generation. in, Input signal (S) in The absolute value of the peak amplitude (|A) peak |) switches between high and low levels, where the absolute value of the peak amplitude (|A) peak |) is at a low level above zero, or Among them, the absolute value of the peak amplitude (|A) peak |) Oscillates according to the continuous envelope curve.

2. The method according to claim 1, in, The duty cycle (DC) is adjusted during the operation of the plasma generator (14), wherein the duty cycle (DC) is the absolute value of the peak amplitude (|A) peak The absolute value of the peak amplitude during one oscillation period of |A peak |) greater than the ignition voltage (V) ig The connection time (T) on ) proportion.

3. The method according to claim 2, in, During operation of the plasma generator (14), parameters related to the energy input in the substrate (20) are measured, wherein the duty cycle (DC) is adjusted depending on the measured energy input.

4. The method according to any one of claims 1 or 2, in, Input signal (S) in The absolute value of the peak amplitude (|A) peak |) switches between high and low levels, where the absolute value of the peak amplitude (|A) peak The low level of |) is zero.

5. The method according to claim 1 or 2, in, During the shutdown time (T) off — where the absolute value of the peak amplitude (|A) peak |) is less than the ignition voltage (V) ig — During this period, the absolute value of the peak amplitude (|A) peak |) At least for most of the shutdown time, it is above zero.

6. The method according to any one of claims 1 or 2, in, Input signal (S) in Based on having a first frequency (f) base The basic signal (S) base ), of which the basic signal (S) base ) by having a second frequency (f mod The modulation signal (S) mod ) modulation, second frequency (f mod ) lower than the first frequency (f base ).

7. The method according to claim 1 or 2, in, Second frequency (f) mod At most, it is the first frequency (f) base 1 / 20 of ).

8. The method according to claim 1 or 2, in, During the shutdown time (T) off — where the absolute value of the peak amplitude (|A) peak |) is less than the ignition voltage (V) ig —After that, the first frequency (f) base Adjust to the resonant frequency of the plasma generator (14).

9. A piezoelectric plasma generator, comprising: piezoelectric transformers, and A control circuit (15) is used to operate the plasma generator according to the method of any one of claims 1 or 2.

10. The piezoelectric plasma generator according to claim 9, in, The control circuit (15) is configured to provide an input signal (S) to the piezoelectric transformer. in ), The control circuit (15) includes a function for generating a frequency (f) of a first frequency. base The basic signal (S) in The basic signal generator (16) is used to generate a signal with a second frequency (f) mod The modulation signal (S) mod The modulation signal generator (17), the second frequency (f) mod ) less than the first frequency (f base ), and a signal mixer (18) for mixing the base signal (S) in ) and modulated signal (S mod ) mixing, so that the input signal (S) is provided in ), making the input signal (S) in The absolute value of the peak amplitude (|A) peak |) Periodically decrease and increase the ignition voltage (V) of the plasma generator (14) to be less than and greater than the ignition voltage (V) of the plasma generator (14). ig ) level.

11. The piezoelectric plasma generator according to claim 9, in, The control circuit (15) further includes a measuring device (19) for measuring parameters related to the energy input to the substrate (20) being plasma-processed by the plasma generator (14), wherein the modulation signal (S) mod It depends on the measured energy input and is adjusted accordingly.

12. The piezoelectric plasma generator according to claim 9, in, The control circuit (15) is configured to adjust the duty cycle (DC) during operation of the plasma generator (14), the duty cycle (DC) being the absolute value of the peak amplitude (|A) peak The absolute value of the peak amplitude in one oscillation period of |A peak |) greater than the ignition voltage (V) ig The connection time (T) on ) proportion.

13. The piezoelectric plasma generator according to claim 9, Includes a measuring device (19) for measuring the frequency relative to a first frequency (f). base The parameters related to the offset of the resonant frequency of the plasma generator (14).

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