CN1178088C - Electrostatic torsion micromirror with stage structure bottom electrode and method for making same - Google Patents

Abstract

The present invention relates to a static torsion micro lens with a staircase structure bottom electrode. The present invention is characterized in that a driving electrode is in a structure of a multistage step bottom electrode, and the number of steps of the staircase structure bottom electrode is greater than or equal to 2. An angle of a staircase bottom electrode and the micro lens is controlled through a ratio value of step height h and step width l. Torsional beams are respectively arranged along an X direction and a Y direction to carry out two-dimensional nesting and can be conveniently expanded into a two-dimensional rotating micro lens. In a making method, the static torsion micro lens is made by maskless anisotropic etching or by DRIE dry etching or by combining two methods, and then a staircase electrode and the micro lens are aligned and installed. A used material is monocrystalline silicon or an SOI material, and the present invention integrates the advantages of two existing rotating micro lenses with a sloping electrode, and a bottom electrode which is parallel to the micro lens in the prior art.

Description

A kind of electrostatic torsion micro mirror with staircase structure hearth electrode

Technical field

The present invention relates to a kind of electrostatic torsion micro mirror, belong to the rotational micromirror field with staircase structure hearth electrode.

Background technology

The electrostatic torsion micro mirror is to change the light direct of travel, realizes that light path is switched and the effective tool of photoscanning, is widely used in the products such as photoswitch, scanner, camera.

The electrostatic torsion micro mirror generally includes micro mirror 1, turns round beam 2,3 three parts of drive electrode, as shown in Figure 1.Its equation of motion is as follows:

$I\frac{{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">d</figure-callout>}}^2\mathrm{\&theta;}}{{\mathrm{<figure-callout\; id="2"\; label="dt"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">dt</figure-callout>}}^2}+\mathrm{\&eta;}\frac{\mathrm{d\&theta;}}{\mathrm{dt}}+M_r=M_e---\left(1\right)$

In the formula, θ is a windup-degree, and I is a moment of inertia of turning round beam and micro mirror, and η is a ratio of damping, M _rFor turning round the restoring moment of beam, M _eBe electrostatic driving torque.The restoring moment of turning round beam and the material of turning round beam, elasticity coefficient, shape are relevant.Static moment then with the shape of electrode, size, relevant with the distance of micro mirror etc.

Present electrostatic torsion micro mirror mainly contains Fig. 2 and two kinds shown in Figure 3, adopts bulk silicon technological or surface silicon technology to make usually.

In the electrostatic torsion micro-mirror structure of Fig. 2, hearth electrode is parallel with micro mirror, and its static moment is:

$M_e=\frac{{\mathrm{\&epsiv;}}_0{V}^2\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">L</figure-callout>}}{{2\mathrm{\&theta;}}^2}\&lsqb;\ln \left(\frac{x-\frac{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">D</figure-callout>}}{2}\sin \mathrm{\&theta;}}{x\cos \mathrm{\&theta;}-d_0\sin \mathrm{\&theta;}}\right)+\frac{x}{x-\frac{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">D</figure-callout>}}{2}\sin \mathrm{\&theta;}}-\frac{x}{x\cos \mathrm{\&theta;}-d\sin \mathrm{\&theta;}}\&rsqb;---\left(2\right)$

L is a micro mirror length in the formula, and x is the distance of hearth electrode and micro mirror, and D is the distance of electrode distal-most end, and V is a driving voltage, d ₀Distance for micro mirror center and electrode limit.

The making of this electrostatic torsion micro mirror is comparatively simple, but because hearth electrode and micro mirror are far away at interval, and driving voltage is bigger, the angle of inclination is subjected to the restriction of minute surface size and minute surface hearth electrode spacing in addition.

Fig. 3 adopts the inclination hearth electrode, because hearth electrode and micro mirror distance reduce, driving voltage is lower, and the angle of inclination is subjected to less restriction simultaneously.In addition, the support under the micro mirror can limit the motor pattern of micro mirror, avoids structure to cause damaging because of over-large displacement.Its electrostatic driving torque is:

$M_e=\frac{{\mathrm{\&epsiv;}}_0{V}^{2}L}{2{(\mathrm{\&alpha;}-\mathrm{\&theta;})}^2}\ln \left(\frac{x}{d\sin \mathrm{\&alpha;}}\right)---\left(3\right)$

The same equation of parameter (1) and (2) in the formula.

But the making of inclined electrode at present generally is to adopt body silicon wet corrosion technique to make, and can only utilize crystal face to obtain some fixing angles, can not satisfy multiple needs.The inclined electrode that adopts other method to make needs special processing and installation, is unfavorable for that large-scale production is to reduce cost.

Summary of the invention

The present invention proposes a kind of electrostatic torsion micro-mirror structure with ladder hearth electrode, adopts wet etching or dry etching method to make the ladder hearth electrode.The mirror of turning round that adopts the present invention to produce needs less driving voltage, can make in enormous quantities, and hearth electrode conveniently is designed to multiple angles simultaneously, as the analog or digital purposes.

The electrostatic torsion micro mirror that the present invention has step electrode is multistage staircase structure, and concrete structure is referring to Fig. 4.Its basic structure is that the inclination hearth electrode among Fig. 3 is replaced with multistage step, and each step can be regarded one group of parallel pole among Fig. 2 as.Obviously, the present invention will have the advantage of Fig. 2 and Fig. 3 design concurrently like this.

Electrostatic driving torque of the present invention is:

$M_e=\frac{{\mathrm{\&epsiv;}}_0{V}^2\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">L</figure-callout>}}{{2\mathrm{\&theta;}}^2}\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}\&lsqb;\ln \left(\frac{x_i-\frac{d_i+\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">l</figure-callout>}}{2}\sin \mathrm{\&theta;}}{x_i\cos \mathrm{\&theta;}-d_i\sin \mathrm{\&theta;}}\right)+\frac{x_i}{x_i-\frac{d_i+\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="C0113928700102.png"\; state="\{\{state\}\}">l</figure-callout>}}{2}\sin \mathrm{\&theta;}}-\frac{x_i}{x_i\cos \mathrm{\&theta;}-d_i\sin \mathrm{\&theta;}}\&rsqb;---\left(4\right)$

X in the formula _i=x ₀+ ih, d _i=d ₀+ il.x ₀Be the distance of micro mirror and first order step, θ is the micro mirror windup-degree, and h is a bench height, and l is a step width, and n is a number of steps.

Staircase structure hearth electrode of the present invention has three parameters: height h, width l, number of steps n.That is with these three parameter characterizations.Wherein the ratio of height h and width l can be controlled the angle of inclination of micro mirror, and number of steps n is mainly determined by process conditions.But, then become inclined electrode as n=1 at least more than or equal to 2.Can carry out design flexible by regulating these three parameters, satisfy various requirement.

The present invention relates to ladder hearth electrode and micro mirror and can utilize the combination of no mask anisotropy rot etching method or deep reaction ion etching (DRIE) method or two kinds of methods to make, material can be selected monocrystalline silicon or SOI (silicon on the insulation course) material for use.At last micro mirror and step electrode are aimed at, installed, make electrostatic torsion micro mirror with multistage staircase structure hearth electrode.

Now details are as follows respectively with concrete method for making:

1. maskless anisotropic etch legal system is made the step electrode concrete steps and is:

(1) silicon (SOI) material oxidation on monocrystalline silicon piece that (100) are orientated or the insulation course, oxidated layer thickness is the 0.5-1.5 micron;

(2) photoetching, corrosion oxidation silicon form the mask graph of multistage ladder;

(3) grown silicon nitride layer, thickness is between the 200-400 nanometer;

(4) adopt TMAH (Tetramethylammonium hydroxide) mordant, concentration is 20-40% (weight ratio), and temperature is 80-90 ℃, or adopts the KOH mordant, and concentration is 40-80% (weight ratio), and temperature is 40-90 ℃, corrosion 0.6-0.9 micron;

(5) photoetching, corrosion oxidation silicon are removed the part mask;

(6) adopting Tetramethylammonium hydroxide or KOH to corrode to structure finishes again.

2. maskless anisotropic etch legal system is made the micro mirror processing step and is:

(1) monocrystalline silicon piece or the SOI material oxidation that (100) are orientated, oxidated layer thickness 0.5-1.5 micron;

(2) growth 50-150 nano silicon nitride silicon layer is with stress equilibrium;

(3) photoetching, corroding silicon nitride and silicon oxide layer form micro mirror and turn round the mask graph of beam;

(4) reverse side photoetching silicon chamber mask;

(5) adopt the Tetramethylammonium hydroxide mordant, concentration is 20-40% (weight ratio), and temperature is 80-90 ℃, or adopts the KOH mordant, and concentration is 40-80% (weight ratio), and temperature is 40-90 ℃, corrosion 0.6-0.9 micron;

(6) in HF, remove silicon oxide layer;

(7) gold or aluminium are steamed in the micro mirror surface, and thickness is at the 0.1-1 micron, and purpose increases reflectivity.

3. the concrete steps of dry etching step electrode are:

(1) oxidation 0.5-1.5 micron on monocrystalline silicon or SOI material;

(2) photoetching, employing wet etching silicon oxide layer, the mask graph of formation first order step;

(2) photoetching, employing wet etching silicon oxide layer, the mask graph of formation first order step;

(3) dry etching 1.5-3 micron;

(4) the rest may be inferred, until desired structure.

4. the concrete steps of dry etching making micro mirror are:

(1) oxidation 0.5-1.5 micron on monocrystalline silicon or SOI material;

(2) growth 80-120 nano silicon nitride silicon layer;

(3) photoetching, etch silicon nitride and silicon oxide layer form micro mirror and turn round the mask graph of beam;

(4) front dry etching 1.5-3 micron;

(5) with silicon chip oxidation again or positive grown silicon nitride;

(6) reverse side photoetching silicon chamber mask;

(7) adopt the Tetramethylammonium hydroxide mordant, concentration is 20-40% (weight ratio), and temperature is 80-90 ℃, or adopts the KOH mordant, and concentration is 40-80% (weight ratio), and temperature is 40-90 ℃, corrosion 0.6-0.9 micron;

(8) gold, aluminium are steamed in the micro mirror surface, and thickness is at the 0.1-1 micron.

The basic structure that the present invention proposes is the one dimension rotational micromirror shown in figure one, turns round beam and carries out that bidimensional is nested to expand to two-dimentional rotational micromirror by being provided with respectively in directions X and Y direction.

Obviously, advantage of the present invention is as follows:

1. to have a driving voltage lower for the micro mirror of the present invention's staircase structure hearth electrode, the advantage that power consumption is less.Because step electrode has reduced the distance between electrode and the micro mirror, can significantly reduce the driving voltage of micro mirror.

2. the restriction of the movement angle of the micro mirror of the present invention's staircase structure hearth electrode is less, conveniently carries out the design of multiple angles.Because do not have the restriction relation of distance between micromirror movements angle in figure two design and micro mirror and hearth electrode, this kind micro mirror can carry out the design of bigger movement angle under identical driving voltage.

3. the present invention's staircase structure hearth electrode micro mirror can provide bottom support to micro mirror, thereby has limited the unwanted motor pattern of micro mirror, avoids one-piece construction because of the damage that over-large displacement causes, and has improved reliability of structure.

4. the present invention's structure fabrication is a two dimensional surface technology, is fit to large-scale production to reduce cost.

5. the present invention's micro mirror adopts monocrystalline silicon to make, and has flatness and luminance brightness preferably, the reflectivity height.

Description of drawings

The conventional electrostatic torsion micro-mirror structure of Fig. 1 synoptic diagram

The electrostatic torsion micro-mirror structure synoptic diagram that Fig. 2 hearth electrode is parallel with micro mirror

Fig. 3 adopts the electrostatic torsion micro mirror synoptic diagram of inclined electrode

Fig. 4 electrostatic torsion micro-mirror structure synoptic diagram with step electrode provided by the invention

Among the figure 1: micro mirror, 2: turn round beam, 3: common drive electrode, 4: incline structure drive electrode, 5: staircase structure drive electrode, θ: windup-degree, x: be the distance of hearth electrode and micro mirror, D: the distance of electrode distal-most end, d ₀: the distance on micro mirror center and electrode limit, x ₀: the distance of micro mirror and first order step, h: bench height, l: step width

Embodiment

Embodiment 1

Adopt anisotropy not have masking method and make micro mirror with two-layer step electrode

Parameter is: monolateral 1000 microns of the beam lengths of turning round, and 500 microns of the square mirror length of sides, windup-degree is 1 degree to the maximum.

Design number of steps n=4, height h=2 micron, length l=115 micron.

The step electrode technological process is as follows:

1. with the monocrystalline silicon piece oxidation of (100) orientation, oxidated layer thickness is 1 micron.

2. photoetching, corrode silicon dioxide, formation can be satisfied the mask pattern that multistage ladder does not have the mask corrosion technological requirement.

3. grown silicon nitride, thickness is in 300 nanometers.

4. adopt 0.8 micron of 50 ℃ of corrosion of 50%KOH.

5. photoetching, corrode silicon dioxide are removed the part mask.

6. adopt 50%KOH to erode to needed result again for 50 ℃.

The micro mirror technological process is as follows:

1. the soi wafer oxidation of the device layer that monocrystalline silicon (100) is orientated, oxidated layer thickness is 1 micron.

2. grow 100 nano-silicon nitrides with equilibrium stress.

3. photoetching, corrosion device layer silicon nitride and silicon dioxide form micro mirror and turn round the mask pattern of beam.

4. reverse side photoetching silicon chamber mask is to discharge the silicon mirror.

5. adopt 50 ℃ of anisotropic etchs of 50%KOH to finish to structure.

6. in HF, remove silicon oxide layer.

7. 1 micron of gold is steamed on the micro mirror surface.

At last, step electrode and micro mirror are aimed at, installed.

Embodiment 2

Adopt anisotropy not have masking method and make micro mirror with two-layer step electrode

Parameter is: monolateral 1000 microns of the beam lengths of turning round, and 500 microns of the square mirror length of sides, windup-degree is 1 degree to the maximum.

Design number of steps n=4, height h=2 micron, length l=115 micron.

The concrete making step of dry etching step electrode is as follows:

1. with 1 micron of oxidation on the silicon chip.

2. photoetching, employing wet etching monox, the mask pattern of formation first order step.

3. dry etching is 2 microns.

4. photoetching, employing wet etching monox, the mask pattern of formation second level step.

5. dry etching is 2 microns.

6. photoetching, employing wet etching monox, the mask pattern of formation third level step.

7. dry etching is 2 microns.

Adopt the concrete steps of dry etching making micro mirror as follows:

1. with 1 micron of soi wafer oxidation.

2. grown silicon nitride is 100 microns.

3. photoetching, etch silicon nitride and silicon dioxide form micro mirror and turn round the mask pattern of beam.

4. the front dry etching goes out micro mirror and turns round beam.

5. front protecting.

6. reverse side photoetching silicon chamber mask is to discharge the silicon mirror.

7. adopt the KOH anisotropic etch to finish to structure.

8. 1 micron of metallic aluminium is steamed on the micro mirror surface.

At last, step electrode and micro mirror are aimed at, installed.

Claims (3)

1. the electrostatic torsion micro mirror with staircase structure hearth electrode comprises micro mirror (1), turns round beam (2), it is characterized in that drive electrode is multistage ladder bottom electrode structural; Electrostatic driving torque is:

$M_e=\frac{{\mathrm{\&epsiv;}}_0{V}^{2}L}{{2\mathrm{\&theta;}}^2}\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}[1n\left(\frac{x_i-\frac{d_i+l}{2}\sin \mathrm{\&theta;}}{x_i\cos \mathrm{\&theta;}-d_i\sin \mathrm{\&theta;}}\right)+\frac{x_i}{x_i-\frac{d_i+l}{2}\sin \mathrm{\&theta;}}-\frac{x_i}{x_i\cos \mathrm{\&theta;}-d_i\sin \mathrm{\&theta;}}]$

X in the formula _i=x ₀+ ih, d _i=d ₀+ il, x ₀Be the distance of micro mirror and first order step, θ is the micro mirror windup-degree, and h is a bench height, and l is a step width, and n is a number of steps.

2. by the described electrostatic torsion micro mirror with staircase structure hearth electrode of claim 1, it is characterized in that number of steps n at least more than or equal to 2, its number is determined by process conditions; The angle of ladder hearth electrode and micro mirror is by the ratio control of height h and width l.

3. by claim 1 or 2 described electrostatic torsion micro mirrors with staircase structure hearth electrode, it is characterized in that being provided with respectively and turn round beam and carry out two dimension nested by directions X and Y direction, expand to two-dimentional rotational micromirror.

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