Thin film structure for micro-bolometer and method for fabricating the same

Abstract

Disclosed is a resistor thin film for micro-bolometer for growth of a vanadium dioxide (VO.sub.2) thin film in monoclinic VO.sub.2 crystal phase by deposition of VO.sub.2 on oxide with perovskite structure and a method for fabricating the same, and the resistor thin film for micro-bolometer according to the present disclosure includes a silicon substrate, an oxide thin film with perovskite structure formed on the silicon substrate, and a VO.sub.2 thin film in monoclinic crystal phase formed on the oxide thin film with perovskite structure.

Claims

1. A resistor thin film for micro-bolometer, comprising: a semiconductor substrate; an oxide thin film with perovskite structure formed on the semiconductor substrate; and a vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase formed on the oxide thin film with perovskite structure.

2. The resistor thin film for micro-bolometer according to claim 1, wherein the semiconductor substrate is one of a silicon substrate, a GaAs substrate, and a sapphire substrate, and when the semiconductor substrate is a silicon substrate, a silicon oxide film is provided on the silicon substrate, and the oxide thin film with perovskite structure is formed on the silicon oxide film.

3. The resistor thin film for micro-bolometer according to claim 1, wherein the vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase is formed with a thickness of 40 to 100 nm.

4. The resistor thin film for micro-bolometer according to claim 1, wherein the oxide thin film with perovskite structure is formed with a thickness of 5 to 20 nm.

5. The resistor thin film for micro-bolometer according to claim 1, wherein the oxide thin film with perovskite structure is made of one of CaTiO.sub.3, LaAlO.sub.3, BaTiO.sub.3, SrTiO.sub.3, SrRuO.sub.3 and BiFeO.sub.3.

6. The resistor thin film for micro-bolometer according to claim 1, wherein the vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase has a temperature coefficient of resistance (TCR) absolute value of 3%/K or more and a specific resistance value of 1 cm or less.

7. A method for fabricating a resistor thin film for micro-bolometer, comprising: preparing a semiconductor substrate; stacking an oxide thin film with perovskite structure on the semiconductor substrate; and forming a vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase on the oxide thin film with perovskite structure.

8. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein in the forming of a vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase on the oxide thin film with perovskite structure, during deposition of vanadium dioxide (VO.sub.2), monoclinic VO.sub.2 crystal phase similar to a lattice structure of the oxide with perovskite structure has a preferred orientation among various crystal phases of vanadium dioxide (VO.sub.2).

9. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the forming of a vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase on the oxide thin film with perovskite structure uses a sputtering process in which a sputtering target is vanadium dioxide (VO.sub.x) in monoclinic crystal phase, a process pressure is set to 5 to 20 mTorr, a process temperature is set to 200 to 500 C., and mixed gas of O.sub.2 and Ar is supplied into a sputtering chamber at a ratio of O.sub.2/(Ar+O.sub.2)=0.2 to 0.3%.

10. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the forming of a vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase on the oxide thin film with perovskite structure uses a reactive sputtering process in which a sputtering target is vanadium metal and reactive gas including O.sub.2 is supplied into a chamber.

11. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the oxide thin film with perovskite structure is made of one of CaTiO.sub.3, LaAlO.sub.3, BaTiO.sub.3, SrTiO.sub.3, SrRuO.sub.3, and BiFeO.sub.3.

12. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase is formed with a thickness of 40 to 100 nm, and the oxide thin film with perovskite structure is formed with a thickness of 5 to 20 nm.

13. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the vanadium dioxide (VO.sub.2) thin film in monoclinic crystal phase has a temperature coefficient of resistance (TCR) absolute value of 3%/K or more and a specific resistance value of 11 cm or less.

14. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the semiconductor substrate is one of a silicon substrate, a GaAs substrate and a sapphire substrate, and when the semiconductor substrate is a silicon substrate, a silicon oxide film is provided on the silicon substrate, and the oxide thin film with perovskite structure is formed on the silicon oxide film.

15. The method for fabricating a resistor thin film for micro-bolometer according to claim 7, wherein the stacking an oxide thin film with perovskite structure on the semiconductor substrate is performed at room temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart illustrating a method for fabricating a resistor thin film for micro-bolometer according to an embodiment of the present disclosure.

(2) FIG. 2 is a configuration diagram of a resistor thin film for micro-bolometer according to an embodiment of the present disclosure.

(3) FIG. 3 is a reference diagram showing a lattice structure of monoclinic VO.sub.2 crystal phase.

(4) FIGS. 4A and 4B show X-ray diffraction analysis results of a monoclinic VO.sub.2/SrTiO.sub.3 thin film fabricated through experimental example 1.

(5) FIG. 5 is a graph showing resistance changes in response to temperature changes of a vanadium dioxide (VO.sub.x) thin film in monoclinic crystal phase fabricated through experimental example 1.

(6) FIG. 6 is a graph showing resistance changes in response to temperature changes in ten times repeated experiments for a vanadium dioxide (VO.sub.x) thin film in monoclinic crystal phase fabricated through experimental example 1.

DETAILED DESCRIPTION

(7) The present disclosure presents technology about a resistor thin film of a micro-bolometer that changes temperature changes to resistance changes.

(8) As mentioned in the description of the related art, a resistor thin film of a micro-bolometer needs to have low resistance itself as well as a high temperature coefficient of resistance (TCR). The monoclinic VO.sub.2 crystal phase has a TCR absolute value of 3%/K or more and a specific resistance value of 10 cm or less, satisfying the requirements as a resistor thin film of a micro-bolometer, but is sensitive to deposition conditions, and thus is difficult to grow in homogeneous phase.

(9) The present disclosure presents technology to stably grow a vanadium dioxide (VO.sub.2) thin film in monoclinic VO.sub.2 crystal phase by deposition of VO.sub.2 on an oxide thin film with perovskite structure.

(10) The oxide with perovskite structure and the monoclinic VO.sub.2 crystal phase have similar lattice structures, and thus, in the deposition of VO.sub.2 on the oxide thin film with perovskite structure, monoclinic VO.sub.2 crystal phase has a preferred orientation among various crystal phases of VO.sub.2. As above, the monoclinic VO.sub.2 crystal phase with a preferred orientation is grown on the oxide thin film with perovskite structure, thereby stably growing a monoclinic VO.sub.2 thin film in homogeneous phase.

(11) Hereinafter, a resistor thin film for micro-bolometer and a method for fabricating the same according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. First, a method for fabricating a resistor thin film for micro-bolometer according to an embodiment of the present disclosure will be described.

(12) Referring to FIGS. 1 and 2, a substrate 210 is prepared (S101), and an insulation film 220 is formed on the substrate 210 at the thickness of about 100 nm (S102). For the substrate 210, a semiconductor substrate such as a silicon substrate may be used, and besides a silicon substrate, a GaAs substrate and a sapphire substrate may be also used. When a silicon substrate is used, the insulation film 220 may include a silicon oxide film (SiO.sub.x).

(13) Subsequently, an oxide thin film 230 with perovskite structure is stacked on the insulation film 220, for example, the silicon oxide film 220 (S103). The perovskite structure oxide thin film 230 has a function of selecting the crystal structure of vanadium oxide as a buffer layer. Only the VO.sub.2 phase is selectively formed among various phases of the vanadium oxide to greatly improve the TCR and decrease the resistivity.

(14) The oxide thin film 230 with perovskite structure may be made of one of CaTiO.sub.3, LaAlO.sub.3, BaTiO.sub.3, SrTiO.sub.3, SrRuO.sub.3 and BiFeO.sub.3, and may be formed through a physical vapor deposition or plasma-enhanced chemical vapor deposition (PECVD) method such as sputtering, pulsed laser deposition (PLD), and e-beam evaporation. The oxide thin film 230 with perovskite structure is preferably formed with the thickness of 5-20 nm.

(15) The deposition process of the oxide thin film 230 having the perovskite structure can be performed at a temperature range of 25 to 700 C. Since the performance of the bolometer is hardly changed within this range, growth at room temperature is also possible.

(16) In a state that the oxide thin film 230 with perovskite structure is formed, a vanadium dioxide (VO.sub.x) thin film 240 in monoclinic crystal phase is formed on the oxide thin film 230 with perovskite structure at the thickness of 40-100 nm using a sputtering method (S104). In the sputtering process, a sputtering target is vanadium dioxide (VO.sub.x) in monoclinic crystal phase, the process pressure is set to 5-20 mTorr, the process temperature is set to 200-500 C., and mixed gas of O.sub.2 and Ar is supplied into a sputtering chamber at a ratio of O.sub.2/(Ar+O.sub.2)=0.2-0.3%.

(17) The deposition temperature of the material is an important factor in the fabrication of the bolometer. If the deposition temperature is high, it damages the ROIC substrate, so that even if the material performance is good, the bolometer may become useless. In the present invention, the deposition process can be performed at a relatively low temperature of 200 to 500 C., which is highly scalable.

(18) In the course of the sputtering process, because the lattice structure of the oxide with perovskite structure and the lattice structure of the monoclinic VO.sub.2 crystal phase are similar to each other, among various crystal phases of VO.sub.2, monoclinic VO.sub.2 crystal phase with a preferred orientation is grown on the oxide thin film 230 with perovskite structure. Through this, the vanadium dioxide (VO.sub.x) thin film 240 in homogeneous monoclinic crystal phase may be formed on the oxide thin film 230 with perovskite structure. For reference, the lattice structure of the monoclinic VO.sub.2 crystal phase is as shown in FIG. 3.

(19) Additionally, a vanadium dioxide (VO.sub.x) thin film in monoclinic crystal phase may be also formed through a reactive sputtering process. In this case, a sputtering target is a vanadium (V) metal target, O.sub.2 is supplied into the chamber, inducing the bond of sputtered vanadium ion (V.sup.+) and oxygen ion (O.sup.2) to form a vanadium dioxide (VO.sub.x) thin film in monoclinic crystal phase.

(20) Besides the sputtering process and the reactive sputtering process described above, the vanadium dioxide (VO.sub.x) thin film 240 in homogeneous monoclinic crystal phase may be also formed on the oxide thin film 230 with perovskite structure through a pulsed laser deposition process.

(21) Through the foregoing process, the fabrication of the resistor thin film for micro-bolometer according to an embodiment of the present disclosure is finished, and the fabricated resistor thin film for micro-bolometer has a stack structure such as shown in FIG. 2.

(22) Hereinafter, the present disclosure will be described in more detail through experimental examples.

Experimental Example 1

Fabrication of Monoclinic VO2/SrTiO3 Thin Film

(23) A VO.sub.2 thin film in monoclinic crystal phase was formed on a SrTiO.sub.3 thin film at the thickness of 54 nm through a sputtering process. A sputtering target was VO.sub.2 in monoclinic crystal phase, and the process pressure was set to 5-20 mTorr, the process temperature was set to 200-500 C., and mixed gas of O.sub.2 and Ar was supplied into a sputtering chamber at a ratio of O.sub.2/(Ar+O.sub.2)=0.2-0.3%.

(24) As a result of conducting X-ray diffraction analysis of the monoclinic VO.sub.2/SrTiO.sub.3 thin film fabricated through experimental example 1, it can be seen that peak for monoclinic VO.sub.2 crystal phase (VO.sub.2(B) in FIG. 4B) appears as shown in of FIG. 4B, and this confirms that VO.sub.2 grown on the SrTiO.sub.3 thin film is monoclinic VO.sub.2 crystal phase. On the contrary, when an oxide thin film with perovskite structure is not used, it can be seen that various crystal phases of vanadium dioxide such as VO.sub.2(A), V.sub.2O.sub.5 and V.sub.3O.sub.7 exist together as shown in of FIG. 4A.

Experimental Example 2

Characteristics of Resistance Change in Response to Temperature Change

(25) FIG. 5 is a graph showing resistance changes in response to temperature changes of the vanadium dioxide (VO.sub.x) thin film in monoclinic crystal phase fabricated through experimental example 1. Referring to FIG. 5, the resistance at room temperature was 44 k, the specific resistance was 0.2 cm or less, and TCR at room temperature was 3.6%/K. Additionally, it can be seen that no hysteresis loop is found in the process of cooling after increasing the temperature of the thin film. This result suggests that the operating temperature range may be extended when a micro-bolometer is fabricated using the vanadium dioxide (VO.sub.x) thin film in monoclinic crystal phase.

(26) Additionally, to identify suitability as bolometer devices, the process of cooling after increasing the temperature of the thin film was performed iteratively 10 times, resistance changes with the temperature change were measured each time (see FIG. 6), and it was found that there was no change in performance.