US3987474A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Non-volatile charge storage elements and an information storage apparatus employing such elements
Assignee: Massachusetts Institute of Technology
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Filing: 1975-01-23
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Granted: 1976-10-19
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Expires: 1995-01-23
Abstract
Abstract A non-volatile charge storage element wherein long-term charge storage occurs in the interface states of the element. Charge is stored at low applied voltages (≦ 10 volts) in short times (≦ 1 microseconds) and is stored as long as 10 5 seconds or longer. The states are emptied by exposure to radiation in the visible or the near infrared regions of the spectrum. There are described, also, an information storage device employing a plurality of such elements and a solid-state camera wherein the image screen includes a plurality of such elements. Changes in the charge storage in each of the elements results in changes in the capacitance of the element; either the capacitance of the element or its charge state is sensed to indicate the state of the element for information storage purposes. In one embodiment, thin film techniques are employed and a change in transconductance is detected to sense the charge state.
Inventors
- 👤 Laurence G. Walker
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 02:09
CPC Classifications
H; H10; H10D; H10D62/00; H10D62/80; H10D62/86; G; G11; G11C; G11C16/00; G11C16/02; G11C16/04; G11C16/0466; H10D1/00; H10D1/60; H10D1/62; H10D1/66; H10F; H10F30/00; H10F30/20; H10F30/21; H10F30/22; H10F30/28; H10F30/282; H10F39/00; H10F39/10; H10F39/12; H10F39/18; H10F39/184
Claims Analysis
Total Claims: 36
Claim 1
Independent Claim
59 words
A non-volatile charge storage element, that comprises, a wide-gap semiconductor material forming a substrate, a thick insulating layer on the substrate, and a metal layer on the insulating layer such that the insulating layer is sandwiched between the substrate and the metal layer, the band gap of the semiconductor material being at least the order of two electron volts.
Claim 2
Dependent Claim
59 words
A non-volatile charge storage element, that comprises, a wide-gap semiconductor material forming a substrate, a thick insulating layer on the substrate, and a metal layer on the insulating layer such that the insulating layer is sandwiched between the substrate and the metal layer, the band gap of the semiconductor material being at least the order of two electron volts.
Claim 3
Dependent Claim
21 words
A storage element as claimed in claim 1 in which the insulating layer is at least the order of 200A thick.
Claim 4
Dependent Claim
16 words
A storage element as claimed in claim 2 in which the wide-gap semiconductor material is ZnS.
Claim 5
Dependent Claim
30 words
A storage element as claimed in claim 2 in which said insulating layer is a material that has a wider energy gap than the energy gap of the semiconductor material.
Claim 6
Dependent Claim
17 words
A storage element as claimed in claim 4 in which said insulating layer is SiO 2 .
Claim 7
Dependent Claim
25 words
A storage element as claimed in claim 1 in which the semiconductor material has a conductivity of at least the order 10 - 4 mhos/cm.
Claim 8
Dependent Claim
79 words
A storage element as claimed in claim 1 in which the substrate is a thin film substrate and that includes two ohmic contacts to provide lateral current flow through the thin film from one ohmic contact to the other, there being a depletion layer along the path of current flow, which depletion layer widens upon storage of charge in the element so as to effect a change in the transconductance of the thin film between the two ohmic contacts.
Claim 9
Dependent Claim
18 words
A system that comprises a plurality of the storage elements of claim 7 to provide a storage device.
Claim 10
Dependent Claim
16 words
A storage element as claimed in claim 1 having an ohmic contact on the semiconductor substrate.
Claim 11
Dependent Claim
53 words
Apparatus that includes an element as claimed in claim 9 and a source of electric potential connected to apply a pulse between the metal layer and the ohmic contact to store charge at or near the semiconductor-insulating-layer interface, thereby to change the capacitance of the device over a broad range of bias voltages.
Claim 12
Dependent Claim
80 words
A storage element as claimed in claim 4 in which the gap of the semiconductor material is at least the order of 2 electron volts and in which the insulating layer is a single homogeneous material layer having a band gap at least the order of 3 electron volts, the semiconductor material substrate being in direct contact with one surface of the insulating layer and the metal layer being in direct contact with the other surface of the insulating layer.
Claim 13
Dependent Claim
28 words
A storage element as claimed in claim 4 wherein the gap of the material forming the insulating layer is in the range of 6 to 10 electron volts.
Claim 14
Dependent Claim
24 words
A storage element as claimed in claim 11 wherein the material forming the insulator has a conductivity no greater than 10 - 4 mhos/cm.
Claim 15
Dependent Claim
67 words
Apparatus as claimed in claim 10 wherein the element is sensitive to radiation in the visible and infrared region of the electromagnetic spectrum and relaxes from a charged state to an uncharged state when subjected to such radiation above some threshold or photon level, which apparatus includes means to subject the element to radiation above said threshold of photon level, selectively, to effect relaxation of the charge.
Claim 16
Dependent Claim
22 words
A system as claimed in claim 8 that further includes means for sensing any change in the transconductance of individual storage elements.
Claim 17
Dependent Claim
154 words
An information storage device comprising a plurality of individual elements, each element having a stable state and at least one quasi-stable state, means for applying an electric potential to each element, which electric potential operates to change the state of said element from the stable state to said at least one quasi-stable state, there being a change in the capacitance of said element over a broad range of bias voltages from the stable state to the quasi-stable state, and means for sensing the change in capacitance thereby to sense the state of said element, each said element being a non-volatile charge storage element comprising a wide-gap semiconductor material substrate, a thick insulating layer on the substrate, and a metal layer on the insulating layer such that the insulating layer is sandwiched between the substrate and the metal layer, the band gap of the semiconductor material being at least the order of 2 electron volts.
Claim 18
Dependent Claim
154 words
An information storage device comprising a plurality of individual elements, each element having a stable state and at least one quasi-stable state, means for applying an electric potential to each element, which electric potential operates to change the state of said element from the stable state to said at least one quasi-stable state, there being a change in the capacitance of said element over a broad range of bias voltages from the stable state to the quasi-stable state, and means for sensing the change in capacitance thereby to sense the state of said element, each said element being a non-volatile charge storage element comprising a wide-gap semiconductor material substrate, a thick insulating layer on the substrate, and a metal layer on the insulating layer such that the insulating layer is sandwiched between the substrate and the metal layer, the band gap of the semiconductor material being at least the order of 2 electron volts.
Claim 19
Dependent Claim
44 words
An information storage device as claimed in claim 12 in which the insulating layer is at least 200A thick and in which the insulating layer is composed of a material that has a wider energy gap than the energy gap of the semiconductor material.
Claim 20
Dependent Claim
25 words
An information storage device as claimed in claim 17 that further includes means for restoring said element from the quasi-stable state to the stable state.
Claim 21
Dependent Claim
57 words
An information storage device as claimed in claim 18 in which said elements are sensitive to light and change from the quasi-stable state to the stable state in the presence of light above some threshold of photon energy and in which said means for restoring is a source of light adapted to irradiate said plurality of elements.
Claim 22
Dependent Claim
36 words
An information storage device as claimed in claim 19 in which each element has an ohmic contact to the semiconductor substrate, electrical connections to the element being made between the metal layer and the ohmic contact.
Claim 23
Dependent Claim
42 words
An information storage device as claimed in claim 16 in which said means for applying an electric potential comprises first transistor means operable to access a particular element in the device and in which said means for sensing comprises second transistor means.
Claim 24
Dependent Claim
20 words
A device as claimed in claim 19 in which the light is in the visible region of the electromagnetic spectrum.
Claim 25
Dependent Claim
20 words
A device as claimed in claim 19 in which the light is in the infrared region of the electromagnetic spectrum.
Claim 26
Dependent Claim
132 words
An information storage device comprising a plurality of individual elements, each element having a stable state and at least one quasi-stable state, means for applying an electric potential to each element, which electric potential acts to change the state of said element from the stable state to said at least one quasi-stable state, there being a change in the transconductance of said element from the stable state to the quasi-stable state, means for sensing the change in said transconductance thereby to sense the state of said element, each said element being sensitive to light such that each will change from the quasi-stable state to the stable state in the presence of light in the visible and the infrared region of the electromagnetic spectrum, and means to subject said elements to such light.
Claim 27
Dependent Claim
132 words
An information storage device comprising a plurality of individual elements, each element having a stable state and at least one quasi-stable state, means for applying an electric potential to each element, which electric potential acts to change the state of said element from the stable state to said at least one quasi-stable state, there being a change in the transconductance of said element from the stable state to the quasi-stable state, means for sensing the change in said transconductance thereby to sense the state of said element, each said element being sensitive to light such that each will change from the quasi-stable state to the stable state in the presence of light in the visible and the infrared region of the electromagnetic spectrum, and means to subject said elements to such light.
Claim 28
Dependent Claim
118 words
An information storage device as claimed in claim 24 in which each said element is a non-volatile charge storage element comprising a thin-film, wide-gap semiconductor material substrate, a thick insulating layer on the substrate, and a metal layer on the insulating layer such that the insulating layer is sandwiched between the substrate and the metal layer, each element further including two ohmic contacts positioned to provide lateral current flow through the thin film from one ohmic contact to the other, there being a depletion layer along the path of current flow, which depletion layer widens upon storage of charge in the element to effect a change in the transconductance of the thin film between the two ohmic contacts.
Claim 29
Dependent Claim
44 words
An information storage device as claimed in claim 25 in which the insulating layer is at least 200A thick and in which the insulating layer is composed of a material that has a wider energy gap than the energy gap of the semiconductor material.
Claim 30
Dependent Claim
25 words
An information storage device as claimed in claim 25 that further includes means for restoring said element from the quasi-stable state to the stable state.
Claim 31
Dependent Claim
57 words
An information storage device as claimed in claim 27 in which said elements are sensitive to light and change from the quasi-stable state to the stable state in the presence of light above some threshold of photon energy and in which said means for restoring is a source of light adapted to irradiate said plurality of elements.
Claim 32
Dependent Claim
39 words
An information storage device as claimed in claim 25 in which the insulating layer is a material taken from the group consisting essentially of Si 2 O 2 , Al 2 O 3 and Si 3 N 4 .
Claim 33
Dependent Claim
69 words
A non-volatile charge storage element, that comprises, wide-gap semiconductor material means forming a substrate, thick insulating layer means formed on the substrate and a metal layer formed on the insulating layer means such that the insulating layer means is sandwiched between the semiconducting material means and the metal layer, charge storage occurring in the interface states of the element between the semiconductor material means and the insulating layer means.
Claim 34
Dependent Claim
69 words
A non-volatile charge storage element, that comprises, wide-gap semiconductor material means forming a substrate, thick insulating layer means formed on the substrate and a metal layer formed on the insulating layer means such that the insulating layer means is sandwiched between the semiconducting material means and the metal layer, charge storage occurring in the interface states of the element between the semiconductor material means and the insulating layer means.
Claim 35
Dependent Claim
33 words
Apparatus as claimed in claim 30 in which charge storage is effected by applying a low voltage pulse between the substrate and the metal layer and which includes means to apply said pulse.
Claim 36
Dependent Claim
61 words
Apparatus as claimed in claim 31 wherein the element is sensitive to radiation and relaxes from a charged state to an uncharged state when subjected to such radiation above some threshold of photon level, which apparatus includes means to subject the element to radiation above said threshold or photon level to effect relaxation from the charged state to the uncharged state.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-10-19 | 1980-04-19 | 1980-10-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-10-19 | 1984-04-19 | 1984-10-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-10-19 | 1988-04-19 | 1988-10-19 | $7700.00 | Window Closed / Lapsed |