CN202534698U - Ferroelectric tunnel junction room temperature infrared detector - Google Patents

Abstract

The utility model discloses a ferroelectric tunnel junction room temperature infrared detector, which is characterized by comprising a substrate, a metal bottom electrode, a ferroelectric functional layer and a semi-transparent metal upper electrode successively arranged from bottom to top. The process for preparing the infrared detector is as follows. Metal materials are coated on the surface of a flexible film substrate in an evaporation or sputtering mode, so that the flexible film substrate is prepared to be the bottom electrode. Then a PVDF-based polymer film with the thickness thereof to be 1-6 nanometers grows on the surface of the bottom electrode by adopting the Langmiur-Blodgett (LB) method to form the ferroelectric functional layer. After that, the metal upper electrode is prepared on the ferroelectric functional layer in an evaporation or sputtering mode so as to form a ferroelectric tunnel junction. Finally, the substrate is thinned. When the infrared detector is in use, a micro constant current is switched on. The infrared detection is realized through measuring the voltage across the electrode under the illumination condition. The detector can be adjusted in temperature coefficient and polarity according to the requirements of an application environment and a detection object, while the incident radiation does not need to be modulated.

Description

A kind of ferroelectric tunnel junction room temperature infrared detector

Technical field

This patent relates to a kind of non-refrigerated infrared detector technology, specifically refers to a kind of ferroelectric tunnel junction room temperature infrared detector.

Background technology

Infrared detection technique is to the technology of infrared radiation perception output, can be widely used in various fields such as national defence, space flight, medical science, production monitoring.Based on the pyroelectric infrared detector of ferroelectric material in the just commercialization nineties in last century.But at nearly 10 years; Ferroelectric infrared focal plane detector receives the severe challenge based on the microbolometer thermal infrared focus planardetector of vanadium oxide material: the one, and the minimum sensitive unit of ferroelectric detector can only accomplish 50 microns; And the sensitive unit of micro-metering bolometers such as vanadium oxide, amorphous silicon has accomplished 15 microns at present, and this just makes the latter's focal plane resolution be superior to the former greatly; The 2nd, ferroelectric detector work is AC mode, need to use optical chopper that the incident infrared radiation is modulated, and micro-metering bolometer does not need, and makes the latter's cost and reliability be higher than the former.It is different that such result stems from two kinds of device detection principles: what the sensitive unit of ferroelectric detector adopted is capacitor arrangement; For the physical quantity surveyed of infrared radiation response output be when illumination is arranged reference unglazed according to the time condenser charge amount variation, therefore need modulate incident light.Charge density is determined by iron electric polarization character; Therefore total quantity of electric charge variation is proportional to area, and along with sensitive elemental area diminishes, the quantity of electric charge that can survey diminishes; Therefore need between detector sensitivity and resolution, compromise, therefore limit the resolution of detector; And sensitive first unit of bolometers such as vanadium oxide is a pure resistance, and the resistance value size is reaction radiation temperature height directly, the undesired signal modulation.Signal magnitude also and do not have direct correlation between the area.Therefore, compare with micro-metering bolometer, the difficulty that development faced of ferroelectric infrared focal plane detector can't be gone beyond under existing mode of operation.

Progress along with ferroelectric physical development and film preparing technology; Prepare ferroelectric tunnel junction (Ferroelectric tunnel junctions, be called for short FTJs) and become that possible [Science 304,1650 (2004); Appl.Phys.Lett.95; 32903 (2009) .] the .FTJs notion proposes in 1971 by the people such as Esaki of IBM Corporation the earliest, is called polarity switch (polar switch) [IBM Tech.Discl.Bull.13,2161 (1971)] at that time.With respect to traditional tunnel junction; FTJs has a special effect; Exactly when the iron electric polarization direction when varying in size because that polarization causes electrostatic field is different in the distribution of barrier region, and cause the tunnel junction conduction different; This phenomenon is called as the tunnel electricity now and sends a telegraph resistance (tunnel electroresistance is called for short TER) effect.Utilize the different tunnels of iron electric polarization direction junction conduction different, can prepare ferroelectric memory [Nature 460,81 (2009)].Except the TER effect, because iron electric polarization will cause the variation of tunnel junction barrier with variation of temperature, and then cause tunnelling current with variations in temperature, according to this character, we propose a kind of novel ferroelectric tunnel junction room temperature infrared detector.

Summary of the invention

This patent proposes a kind of ferroelectric IR detectro of the employing new infrared detection mode based on ferroelectric tunnel junction, has realized the application of ferroelectric tunnel junction structure in the infrared acquisition field.

Ferroelectric tunnel junction micro-metering bolometer detection principle is following:

According to document [Phys.Rev.Lett.94,246802 (2005)], corresponding to ferroelectric thin film ± two polarized state, the tunnel junction barrier height is:

U＝U ₀±BP， (1)

Wherein, corresponding two polarized states of sign, U ₀Tunnel junction insulating barrier when being polarized to zero for ferroelectric material can be with barrier height, and P is the ferroelectric thin film residual polarization, and (ε, δ d) are two electrode material Thomas-Fermi shielding length δ to B _iThe constant of (i is 1 or 2, represents two electrodes) and ferroelectric insulating barrier DIELECTRIC CONSTANTS and thickness d decision is expressed as:

$B=\frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA0000144722940000011.png"\; state="\{\{state\}\}">d</figure-callout>}}{2{\mathrm{\&epsiv;}}_0}\frac{{\mathrm{\&delta;}}_1-{\mathrm{\&delta;}}_2}{\mathrm{\&epsiv;}({\mathrm{\&delta;}}_1+{\mathrm{\&delta;}}_2)+d}---\left(2\right)$

The tunnel junction tunnelling current can be expressed as [S.M.Sze, " Physics of semiconductor devices ", Wiley, New York (1981)]:

In above formula, J is a tunnelling current density, m ^*Be the effective mass of tunnelling electronics, q is an elementary charge,

Be Planck's constant, E is the electric field strength in interface,

Under the constant voltage mode of operation, can derive by above formula:

Wherein p ' is a ferroelectric layer material pyroelectric coefficient.

Definition according to temperature coefficient of resistance:

α＝ΔR/RΔT

Wherein R is a device resistance, changes in resistance amount when Δ R is variations in temperature Δ T.Utilize relational expression dR/R=-dI/I under the constant voltage mode of operation, get from (4) formula:

Physics constant and Kynoar (PVDF) ferroelectric material parameter substitution formula (5) can simply be estimated ferroelectric tunnel junction resistance temperature coefficient:

q＝1.6×10 ^-19C?m ^*≈9.1×10 ^-31kg?

U ₀≈1.0eV?p′＝2.7×10 ^-5C/Km ²，

E=10 ⁸V/m (0.1 volt is added on the 1 nanometer PVDF)

Suppose δ ₁-δ ₂=0.1nm, B ≈ (δ ₁-δ ₂)/2 ε ₀≈ 6m ²/ F,

Obtain: α _v≈ ± 2 * 10 ^-2(K ^-1),

The temperature coefficient (3.4 * 10 of this temperature coefficient and other micro-metering bolometer material such as vanadium oxides, manganese cobalt nickel material ^-2/ K) suitable.What be different from the latter is, the TCR of ferroelectric tunnel junction is relevant with the working point, and this coefficient and electric field strength are inversely proportional to, and the polarity of temperature coefficient also can change through the iron electric polarization direction.Through the trim working point, can the optimize device performance parameter.

From formula (3) and dV=RdI, can derive also that temperature coefficient of resistance is under the constant current mode of operation:

${\mathrm{\&alpha;}}_i=\frac{{\mathrm{\&alpha;}}_v}{2}/(1+U|{\mathrm{\&alpha;}}_v|/3B{p}^{\&prime;})---\left(6\right)$

Can see that from formula temperature coefficient of resistance is always less than the constant voltage mode of operation under the constant current mode of operation.Even so, owing to can adopt four probe method to reduce the error that the electrode contact causes under the constant current mode of operation, adopt this pattern during therefore actual the use.

The structural design of ferroelectric tunnel junction detector and preparation method:

The detector of above-mentioned patent will be implemented through a kind of novel ferroelectric tunnel junction based on Kynoar (PVDF) ferroelectric polymer material of preparation, and technology is simple, and cost is low; Need not refrigeration; Need not light modulation, the working point is adjustable, but integration is strong and be easy to preparation and become focal plane array device.

A kind of novel ferroelectric tunnel junction of this patent room temperature infrared detector is characterized in that, on substrate 1, is followed successively by hearth electrode 2, ferroelectric functional layer 3 and top electrode 4, wherein:

Described substrate 1 is a fexible film, and thickness is the 1-5 micron;

Described hearth electrode 2 is an aluminium, gold, and silver, platinum, nickel, NI-G, ferronickel metal or alloy, electrode are elongate in shape, thickness is not less than 100 nanometers;

The PVDF base ferroelectric polymer film that described ferroelectric functional layer 3 is the 1-6 nano thickness;

Described top electrode 4 is an aluminium, gold, and silver, platinum, nickel, NI-G, ferronickel metal or alloy, thickness of electrode are about the pellicle of 20-50 nanometer, and top electrode (4) is right-angled intersection with hearth electrode (2).

This patent a kind of novel ferroelectric tunnel junction room temperature infrared detector and preparation method is characterized in that, the device preparation may further comprise the steps: growing metal hearth electrode 2 ferroelectric functional layers 3 and half are passed through electrode of metal 4 successively on substrate 1.

Concrete preparation process is:

(1) hearth electrode preparation

The evaporativity layer of metal film is as hearth electrode on the fexible film substrate of thickness 1-5 micron, and electrode is bar shaped, and thickness is not less than 100 nanometers, and electrode can use aluminium, gold, silver, platinum, nickel, NI-G, metal or alloy such as ferronickel.

(2) ferroelectric functional layer preparation

Ferroelectric functional layer is a PVDF base ferroelectric polymer film, and this thin-film material utilization Langmuir-Blodgett method is grown on the substrates such as polyester of hearth electrode.PVDF based powders or block are dissolved in dimethyl sulphoxide solution, adopt the Langmuir-Blodgett method PVDF base ferroelectric polymer film of growing then, film thickness is controlled at the 1-6 nanometer.Based polymer film prepares to be needed 100-150 ℃ of annealing 4 hours after complete.

(3) top electrode preparation

Utilize the evaporation coating method to prepare metal film as top electrode, the very bar shaped that powers on, top electrode need be prepared into pellicle, the about 20-50 nanometer of thickness.Top electrode intersects with hearth electrode, and the part that overlaps is the responsive unit of detector, forms ferroelectric tunnel structure.

(4) attenuate substrate

Utilize the oxygen plasma lithographic technique, the sensitive unit of etching place's flexible substrate material.Through adjustment etching power and time, may command etching speed.The attenuate backing material reduces device calorifics time constant and improves detectivity.

Between upper/lower electrode, feed small constant current, detecting electrode voltage.Under the different emittance illumination, the different iron electric polarization differences of device temperature cause tunnel junction resistance different, realize ferroelectric tunnel junction room temperature infrared detector.

This patent characteristics are to use the ferroelectric tunnel junction based on ferroelectric ultrathin membrane, and the ferroelectric IR detectro principle of this structure is similar to micro-metering bolometer, the predicament that can avoid present business-like ferroelectric ceramic detector focal plane to be faced.

Use the ferroelectric tunnel junction room temperature infrared detector of this patent preparation also to have following advantage:

Detector has according to the demand temperature coefficient of the applied environment and detection of a target size adjustable with polarity, need not characteristic such as is modulated in the incident radiation source.This detector preparation technology is simple relatively, cost is low, environmental friendliness.This detector is prone to preparation and becomes array element, can realize the infrared target radiographic measurement.

Description of drawings:

Fig. 1 is a detector cross section structure sketch map;

Among the figure, 1 substrate, 2 hearth electrodes, 3 ferroelectric functional layers, 4 top electrodes.

Embodiment:

To be to combine accompanying drawing 1 below, the practical implementation method of statement this patent:

(1) polyester film of selecting 2.5 microns of thickness for use is as substrate.

(2) hearth electrode preparation

Vapor deposition layer of metal aluminium film is as hearth electrode on substrate film, and electrode is bar shaped, and width is 100 microns, thickness 100 nanometers.

(3) ferroelectric functional layer preparation

This thin-film material utilization of P (VDF-TrFE) Langmuir-Blodgett method is grown on the substrates such as polyester of hearth electrode.(VDF-TrFE, 70: 30mol%) be dissolved in dimethyl sulphoxide solution, adopt Langmuir-Blodgett method P (VDF-TrFE) thin polymer film of growing then, film thickness is respectively 1,3 and 6 nanometers with P.

(4) top electrode preparation

Utilize evaporation coating to prepare the aluminium film, form capacitor arrangement as top electrode.The very bar shaped that powers on, width is 100 microns, and top electrode need prepare becomes pellicle, and thickness is 20 nanometers, can use aluminium, gold, silver, platinum, nickel, NI-G, metal or alloy such as ferronickel, top electrode intersects with hearth electrode, and the part that overlaps forms ferroelectric tunnel junction structure.

(5) substrate thinning

Utilize the oxygen plasma lithographic technique, below, etching sensitive unit zone backing material, polyester film or polyimide film, etching power 300W and time are 2 minutes, polyester substrate material that can etching 1.5 micron thickness.

(6) between upper/lower electrode, feed small constant current, detecting electrode voltage.Under the different emittance illumination, the different iron electric polarization differences of device temperature cause tunnel junction resistance different, and three devices have all detected voltage response, realize ferroelectric tunnel junction room temperature infrared detector.

Claims (1)

1. a ferroelectric tunnel junction room temperature infrared detector is characterized in that, on substrate (1), is followed successively by hearth electrode (2), ferroelectric functional layer (3) and top electrode (4), wherein:

Described substrate (1) is that polyester film or polyimide film fexible film, thickness are the 1-5 micron;

Described hearth electrode (2) is an aluminium, gold, and silver, platinum, nickel, NI-G, ferronickel metal or alloy, electrode are elongate in shape, thickness is not less than rice in 100;

Described ferroelectric functional layer (3) is the PVDF base ferroelectric polymer film of 1-6 nano thickness;

Described top electrode (4) is an aluminium, gold, and silver, platinum, nickel, NI-G, ferronickel metal or alloy, thickness of electrode are about the pellicle of 20-50 nanometer, and top electrode (4) is right-angled intersection with hearth electrode (2).

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