JPH026654Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a surface acoustic wave oscillator in which surface acoustic wave delay elements used as a reference oscillator and a temperature measurement oscillator are respectively set on the same substrate.

(Prior Art) FIG. 1 shows a block diagram of a surface acoustic wave oscillator, in which 1 is a surface acoustic wave delay element, 2 is an amplifier, the gain of the amplifier is G, the amount of phase delay is φ _A , When the loss of the surface acoustic wave delay element is IL and the amount of phase delay is φ _S , oscillation occurs according to the following equation (1).

GIL φ _A +φ _S =2nπ (n: integer) (1) In equation (1), the oscillation frequency is taken as the oscillation frequency, and the amount of change Δ in the oscillation frequency due to temperature is expressed by equation (2).

Δ=×(−TCD)×ΔT (2) Here, TCD is the delay amount temperature coefficient of the surface acoustic wave delay element, and ΔT is the temperature difference.

(Problems to be solved by the invention) In the case of a general surface acoustic wave delay element, the temperature coefficient of delay TCD is determined by the piezoelectric substrate material used, the cut angle, and the propagation direction of the surface acoustic wave,
In the case of a layered surface acoustic wave element, it is known that the thickness also depends on the thickness of the surface layer. Conventionally, temperature measurements have been performed using a surface acoustic wave oscillator, taking advantage of the fact that the temperature coefficient of delay TCD of this surface acoustic wave is relatively large. However, in order to measure the amount of change △ in the oscillation frequency, the accuracy of temperature measurement is determined by the accuracy of the reference oscillator to be compared.
The reference oscillator needs to be highly accurate, which has the disadvantage of being relatively expensive.

(Means for Solving the Problems) In order to eliminate such drawbacks, the present invention provides a reference oscillator delay line on the same substrate as the surface acoustic wave delay element of the temperature measurement oscillator. By forming the wave delay line into a layered structure and by varying the thickness of the surface layer of the two delay elements on the substrate,
The structure is such that there is a difference in the delay amount temperature coefficient TCD. A detailed explanation will be given below with reference to the drawings.

(Embodiment) Fig. 2 is a perspective view of an embodiment of the present invention, in which 11 is a piezoelectric substrate, 12 is an input/output blind electrode for a reference oscillator, and 13 is an input/output blind electrode for a temperature measurement oscillator, as shown in the figure. They are provided on the same piezoelectric substrate 11. Further, 14 and 15 are amplifiers for a reference oscillator and a temperature measurement oscillator, respectively.

Further, the layer 16 on the piezoelectric substrate 11 is a SiO ₂ film, and the input/output interdigital electrodes 12 and 13 have different film thicknesses and have different delay amount temperature coefficients TCD.

Now, if the delay amount temperature coefficients of the input/output interdigital electrodes 12 and 13 are TCD _Re and TCD _tnp , the reference oscillator is the input/output interdigital electrode 12 and the amplifier 1.
4, oscillation occurs under the condition of equation (1).

Further, the temperature measuring oscillator oscillates by the input/output interdigital interdigital electrode 13 and the amplifier 15 under the condition of equation (1). The amount of change in the oscillation frequency _{△ Re} , △ _tnp due to the temperature difference △T between the oscillation frequencies _Re , _tnp of these two oscillators is determined by equation (2) as follows: △ _Re = _Re × (-TCD _Re ) × △T... ...(3) △ _tnp = _tnp × (−TCD _tnp ) × △T ... (4). Also, from equations (4) and (3), △ _tnp −△ _Re = { _tnp × (−TCD _tnp ) − _Re × (−TCD _Re )}×△T ...(5), and the reference oscillator and temperature measurement oscillator It can be seen that the difference in the amount of change in the oscillation frequency is proportional to the temperature difference ΔT.

As mentioned above, in this invention, the delay lines of the two oscillators are provided on the same board, so the temperature difference between the two delay lines is extremely small, so the accurate temperature can be determined regardless of the temperature stability of the reference oscillator itself. Measurement becomes possible.

As an example, when a SiO ₂ film is deposited on a Z-cut, Y-direction propagation lithium niobate substrate,
The film thickness is kh=2.1 (k: wave number of surface acoustic wave, h:
SiO ₂ film thickness), TCD = 0 and △ _Re =
0, so it is particularly suitable for the delay line of the reference oscillator. Also, the TCD of the board itself with kh=0 is TCD=
76ppm/℃, and by selecting kh=0 to 2.1 as the delay line of the temperature measurement oscillator, △/
By setting /ΔT=-76ppm/°C to 0ppm/°C and kh=2.1 or more, Δ//ΔT can also be set to a positive value. Therefore, if the SiO ₂ film thickness is appropriately selected, the sensitivity of the measurement temperature can be obtained relatively freely.

In addition, the delay element can be easily manufactured by adding a single photo linkage process and a SiO ₂ etching process to simultaneously create a surface acoustic wave delay line for a reference oscillator and for an oscillator with any temperature sensitivity within a certain range. can be produced.

(Effects of the invention) As explained above, the invention provides at least two layered surface acoustic wave elements with different film thicknesses on the same substrate, and the delay time temperature coefficient TCD differs depending on the film thickness. Since the oscillators for reference and temperature measurement are made using Therefore, accurate temperature measurement is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional surface acoustic wave oscillator, and FIG. 2 is a perspective view showing the construction of a surface acoustic wave oscillator according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 11... Piezoelectric substrate, 12... Input/output interdigitated electrode for reference oscillator, 13... Input/output interdigitated electrode for temperature measurement oscillator, 14 and 15... Amplifier, 1
6... _SiO2 thin film.

Claims (1)

[Scope of utility model registration request] In a surface acoustic wave oscillator that uses a layered surface acoustic wave element as a delay element, in which interdigital electrodes are arranged facing each other on a piezoelectric material and a film of a non-piezoelectric material (for example, SiO ₂ ) is attached to the surface of the piezoelectric material, the layered structure elastic Utilizing the fact that the temperature coefficient of delay time of the surface wave element depends on the film thickness of the film, at least two layered structure surface acoustic wave elements having different film thicknesses are formed on the same substrate for reference and temperature measurement. A surface acoustic wave oscillator characterized in that the delay element of each oscillator is used as a delay element.