Reduced surface charging in silicon-based devices

Details Reduced surface charging in silicon-based devices Reduced surface charging in silicon-based devices

2001-01-19

2002-05-14

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

C438S064000, C438S106000

Reexamination Certificate

active

06387723

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to micro-machine devices fabricated from silicon-based materials. Specifically, the invention relates to the surface treatment of silicon-based materials to reduce charge build-up and charge migration.
BACKGROUND OF INVENTION
Grating light valves have applications in display, print, optical and electrical technologies. A grating light valve is a device that is capable of constructively and destructively interfering with an incident light source. Exemplary grating light valves and methods for making grating light valves are disclosed in the U.S. Pat. No. 5,311,360, U.S. Pat. No. 5,841,579 and U.S. Pat. No. 5,808,797, issued to Bloom et al., the contents of which are hereby incorporated by reference.
Grating light valve devices are micro-fabricated from Si-based materials using lithographic techniques. Grating light valve devices are configured to have a plurality of reflective ribbons which are moved by applying an operating bias voltage across the ribbons and a coupled substrate structure. By alternating, or switching, the bias voltage the ribbons are alternated between positions for constructive and destructive interfere with an incident light source having a wavelength &lgr;.
The ribbons of the grating light valves are preferably formed of Si
3
N
4
and the substrate structure is formed of Si or SiO
2
. The surfaces of the ribbons and the substrate tend to be strongly hydrophilic and, thus, readily adsorb, physisorb, or chemi-adsorb water or moisture. Adsorbed, physisorbed, or chemi-adsorbed water or moisture on the operating surfaces of the ribbons and the substrate facilitates surface charging. Charging refers to the undesirable collection and migration electrical charges on the insulating surfaces of the grating light valve. Adsorbed, physisorbed, or chemi-adsorbed water or moisture is a difficult parameter to control within the manufacturing process of grating light valves and can severely diminish the performance of grating light valves.
One application for grating light valves is in the field of imaging and display devices, wherein one or more grating light valves are used create a pixel of an image or a pixel of an image on a display device. The presence of surface charging on the operating surfaces of grating light valves can perturb or shift the switching bias voltages. Thus, some of the grating light valves within the display device do not shut off, turn on and/or produce the desired intensity when a bias voltage is applied. The result is the undesirable persistence of an image, portions thereof or the complete failure of the device to produce the image.
To help ensure that charging is minimized, grating light valve structure are handled and manufactured in moisture free or near moisture free environments. Further, grating light valve structures are hermetically sealed within a die structure, after manufacturing, to maintain a moisture free environment. Processing and storing grating light valve structures in moisture free environments is time consuming and expensive. Further, the steps required to seal grating light structures within a die structure adds several steps to the fabrication process.
What is needed is a method to produce micro-fabricated grating light valve structures that exhibit reduced surface charging. Further what is needed is grating light valve structures that exhibit reduced surface charging in open air environments with typical humidity levels.
SUMMARY OF THE INVENTION
Grating light valves of the instant invention generate the condition for constructive and destructive interference through a plurality of movable ribbons. The movable ribbons provide a first set of reflective surfaces that are movable relative to a second set of reflective surfaces. The second set of reflective surfaces are reflective surfaces on a substrate element or on a second set of ribbons. In operation, an incident light source having a wavelength &lgr; impinges on the first set of reflective surfaces and the second set of reflective surfaces. The movable ribbons are displaced towards or away from the second set of reflective surfaces by &lgr;/4, or a multiple thereof. The portion of light that is reflected from the first set of reflective surfaces and the portion of light that is reflected from the second set of reflective surfaces alternate between being in phase and being out of phase. Preferably, the first set of reflective surfaces and the second set of reflective surfaces are either in the same reflective plane or are separated &lgr;/2 for generating the condition for constrictive interference.
FIG. 1
a
illustrates a grating light valve with plurality of movable ribbons
100
that are formed in a spatial relationship over a substrate
102
. Both the ribbons
100
and the regions of the substrate between the ribbons have reflective surfaces
104
. The reflective surface are provided by coating the ribbons
100
and the substrate with any reflective material such as an aluminum or silver. The height difference
103
between the reflective surfaces
104
on the ribbons
100
and the substrate
102
is &lgr;/2. When light having a wavelength &lgr; impinges on the compliment of reflective surfaces
104
, the portion of light reflected from the surfaces
104
of the ribbons
100
will be in phase with the portion of light reflected from the surfaces
104
of the substrate
102
. This is because the portion of light which strikes the surfaces
104
of the substrate
102
will travel a distance &lgr;/2 further than the portion of light striking the surface
104
of the ribbons
100
. Returning, the portion of light that is reflected from the surfaces
104
of the substrate
102
will travel an addition distance &lgr;/2 further than the portion of light striking the surface
104
of the ribbons
100
, thus allowing the compliment of reflective surfaces
104
to act as a mirror.
Referring to
FIG. 1
b
, in operation the ribbons
100
are displaced toward the substrate
102
by a distance
105
that is equal to &lgr;/4, or a multiple thereof, in order to switch from the conditions for constructive interference to the conditions for destructive interference. When light having a wavelength &lgr; impinges on the reflective surfaces
104
′ and
104
with the ribbons
100
′ in the down position, the portion of light reflected from the surfaces
104
′ will be out of phase, or partially out of phase, with the portion of light reflected from the surfaces
104
and the total reflected light will be attenuated. By alternating the ribbon between the positions shown in
FIG. 1
a
and
FIG. 1
b
, the light is modulated.
An alternative construction for a grating light valve is illustrated in the
FIGS. 2
a-b
. Referring to
FIG. 2
a
, the grating light valve has a plurality of ribbons
206
and
207
that are suspended by a distance
205
over a substrate element
200
. The ribbons
206
and
207
are provided with a reflective surfaces
204
and
205
, respectively. Preferably, the surface
206
of the substrate
202
also are reflective. The first set of ribbons
206
and the second set of ribbons
207
are initially in the same reflective plane in the absence in the applied force. The first set of ribbons
206
and the second set of ribbons
207
are preferably suspended over the substrate by a distance
203
such that the distances between the reflective surfaces of the ribbons
206
and
207
and the reflective surfaces
208
of the substrate
202
are multiples of &lgr;/2. Accordingly, the portions of light reflected from the surfaces
204
and
205
of the ribbons
206
and
207
and the reflective surface
208
of the substrate
202
, with a wavelength &lgr; will all be in phase. The ribbons
206
and
207
are capable of being displaced relative to each other by a distance corresponding to a multiple of &lgr;/4 and thus switching between the conditions for consecutive and destructive interference with an incident light source having a wavelength &lgr;.
In the
FIG. 2
b
, the second set of ribbons
207
are displaced

Affiliated with

Also associated with

Rating

Reduced surface charging in silicon-based devices does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Reduced surface charging in silicon-based devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reduced surface charging in silicon-based devices will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2909961