Document:

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                                                                   Exhibit 10.54
                                                                   -------------

               FIRST AMENDMENT TO CREDIT AND SECURITY AGREEMENT
                                 AND WAIVER OF DEFAULTS

          This Amendment, dated as of March 30, 2001, is made by and between RF
MONOLITHICS, INC., a Delaware corporation (the "Borrower"), and WELLS FARGO BANK
MINNESOTA, N.A., a national banking association (the "Lender").

                                R E C I T A L S

          The Borrower and the Lender have entered into a Credit and Security
Agreement dated as of December 8, 2000 (the "Credit Agreement"). Capitalized
terms used in these recitals have the meanings given to them in the Credit
Agreement unless otherwise specified.

          The Borrower has requested that certain amendments be made to the
Credit Agreement, which the Lender is willing to make pursuant to the terms and
conditions set forth herein.

          NOW, THEREFORE, in consideration of the premises and of the mutual
covenants and agreements herein contained, it is agreed as follows:

          1.   Defined Terms.  Capitalized  terms used in this Amendment which
               -------------
are defined in the Credit Agreement shall have the same meanings as defined
therein, unless otherwise defined herein.

          2.   Amendment to Section 6.15. Section 6.15 of the Credit Agreement
               -------------------------
is amended in its entirety to read as follows:

               Minimum Book Net Worth. The Borrower will maintain, during each
               ----------------------
          period described below, its Book Net Worth in an amount not less than
          the amount set forth below:

               (a)  As of February 28, 2001, a minimum Book Net Worth of not
          less than $29,700,000;

               (b)  From March 1, 2001 through May 31, 2001, a minimum Book Net
          Worth of not less than $29,200,000;

               (c)  From June 1, 2001 through August 31, 2001, a minimum Book
          Net Worth of not less than $29,500,000; and

               (d)  From September 1, 2001 through November 30, 2001, a minimum
          Book Net Worth of not less than the Book Net Worth as of FYE August
          31, 2001, minus $1,500,000.

          3.   Amendment to Section 6.16. Section 6.16 of the Credit Agreement
               -------------------------
 is amended in its entirety to read as follows:

               Quarterly Minimum Net Income. The Borrower will achieve (a)
               ----------------------------
          during the six month fiscal period ended February 28, 2001, a minimum
          Net Income of greater than <$3,000,000>; (b) during the nine month
          fiscal period ending on May 31, 2001, a minimum Net Income of greater
          than <$3,500,000>; (c) during the fiscal year ending on August 31,
          2001, a minimum Net Income of greater than <$3,200,000>; and (d)
          during the three month fiscal period from August 31, 2001, to November
          30, 2001, a minimum Net Income of greater than <$1,500,000>.

          4.   Amendment to Exhibit C. Exhibit C to the Credit Agreement is
               ----------------------
hereby amended to be in the form of Exhibit C to this Amendment.
<PAGE>

          5.   No Other Changes. Except as explicitly amended by this Amendment,
               ----------------
all of the terms and conditions of the Credit Agreement shall remain in full
force and effect and shall apply to any advance or letter of credit thereunder.

          6.   Waiver of Defaults. The Borrower is in default of Sections 6.15,
               ------------------
6.16 and 6.17 of the Credit Agreement (collectively, the "Defaults"). Upon the
terms and subject to the conditions set forth in this Amendment, the Lender
hereby waives the Defaults through February 28, 2001. This waiver shall be
effective only in this specific instance and for the specific purpose for which
it is given, and this waiver shall not entitle the Borrower to any other or
further waiver in any similar or other circumstances.

          7.   Conditions Precedent. This Amendment, and the waiver set forth in
               --------------------
Paragraph 6 hereof, shall be effective when the Lender shall have received an
executed original hereof, together with each of the following, each in substance
and form acceptable to the Lender in its sole discretion:

               (a)  The Acknowledgment and Agreement of Guarantor set forth at
          the end of this Amendment, duly executed by the Guarantor.

               (b)  A Certificate of the Secretary of the Borrower certifying
         as to (i) the resolutions of the board of directors of the Borrower
         approving the execution and delivery of this Amendment, (ii) the fact
         that the articles of incorporation and bylaws of the Borrower, which
         were certified and delivered to the Lender pursuant to the Certificate
         of Authority of the Borrower"s secretary or assistant secretary dated
         as of December 8, 2000 in connection with the execution and delivery of
         the Credit Agreement continue in full force and effect and have not
         been amended or otherwise modified except as set forth in the
         Certificate to be delivered, and (iii) certifying that the officers and
         agents of the Borrower who have been certified to the Lender, pursuant
         to the Certificate of Authority of the Borrower"s secretary or
         assistant secretary dated as of December 8, 2000, as being authorized
         to sign and to act on behalf of the Borrower continue to be so
         authorized or setting forth the sample signatures of each of the
         officers and agents of the Borrower authorized to execute and deliver
         this Amendment and all other documents, agreements and certificates on
         behalf of the Borrower.

               (c)  Such other matters as the Lender may require.

          8.   Representations and Warranties. The Borrower hereby represents
               ------------------------------
and warrants to the Lender as follows:

               (a)  The Borrower has all requisite power and authority to
          execute this Amendment and to perform all of its obligations
          hereunder, and this Amendment has been duly executed and delivered by
          the Borrower and constitutes the legal, valid and binding obligation
          of the Borrower, enforceable in accordance with its terms.

               (b)  The execution, delivery and performance by the Borrower of
          this Amendment have been duly authorized by all necessary corporate
          action and do not (i) require any authorization, consent or approval
          by any governmental department, commission, board, bureau, agency or
          instrumentality, domestic or foreign, (ii) violate any provision of
          any law, rule or regulation or of any order, writ, injunction or
          decree presently in effect, having applicability to the Borrower, or
          the articles of incorporation or by-laws of the Borrower, or (iii)
          result in a breach of or constitute a default under any indenture or
          loan or credit agreement or any other agreement, lease or instrument
          to which the Borrower is a party or by which it or its properties may
          be bound or affected.

               (c)  All of the representations and warranties contained in
          Article V of the Credit Agreement are correct on and as of the date
          hereof as though made on and as of such date, except to the extent
          that such representations and warranties relate solely to an earlier
          date.

                                      -2-
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          9.   References. All references in the Credit Agreement to "this
               ----------
Agreement" shall be deemed to refer to the Credit Agreement as amended hereby;
and any and all references in the Security Documents to the Credit Agreement
shall be deemed to refer to the Credit Agreement as amended hereby.

          10.  No Other Waiver. Except as set forth in Paragraph 6 hereof, the
               ---------------
execution of this Amendment and acceptance of any documents related hereto shall
not be deemed to be a waiver of any Default or Event of Default under the Credit
Agreement or breach, default or event of default under any Security Document or
other document held by the Lender, whether or not known to the Lender and
whether or not existing on the date of this Amendment.

          11.  Release. The Borrower, and the Guarantor by signing the
               -------
Acknowledgment and Agreement of Guarantor set forth below, each hereby
absolutely and unconditionally releases and forever discharges the Lender, and
any and all participants, parent corporations, subsidiary corporations,
affiliated corporations, insurers, indemnitors, successors and assigns thereof,
together with all of the present and former directors, officers, agents and
employees of any of the foregoing, from any and all claims, demands or causes of
action of any kind, nature or description, whether arising in law or equity or
upon contract or tort or under any state or federal law or otherwise, which the
Borrower or such Guarantor has had, now has or has made claim to have against
any such person for or by reason of any act, omission, matter, cause or thing
whatsoever arising from the beginning of time to and including the date of this
Amendment, whether such claims, demands and causes of action are matured or
unmatured or known or unknown.

          12.  Costs and Expenses. The Borrower hereby reaffirms its agreement
               ------------------
under the Credit Agreement to pay or reimburse the Lender on demand for all
costs and expenses incurred by the Lender in connection with the Credit
Agreement, the Security Documents and all other documents contemplated thereby,
including without limitation all reasonable fees and disbursements of legal
counsel. Without limiting the generality of the foregoing, the Borrower
specifically agrees to pay all fees and disbursements of counsel to the Lender
for the services performed by such counsel in connection with the preparation of
this Amendment and the documents and instruments incidental hereto. The Borrower
hereby agrees that the Lender may, at any time or from time to time in its sole
discretion and without further authorization by the Borrower, make a loan to the
Borrower under the Credit Agreement, or apply the proceeds of any loan, for the
purpose of paying any such fees, disbursements, costs and expenses.

          13.  Miscellaneous. This Amendment and the Acknowledgment and
               -------------
Agreement of Guarantor may be executed in any number of counterparts, each of
which when so executed and delivered shall be deemed an original and all of
which counterparts, taken together, shall constitute one and the same
instrument.

          14.  Governing Law; Jurisdiction, Venue; Waiver of Jury Trial. This
               --------------------------------------------------------
Amendment, the Acknowledgment and Agreement of Guarantor and the Loan Documents
shall be governed by and construed in accordance with the substantive laws
(other than conflict laws) of the State of Texas. Each party hereto and the
Guarantor hereby (i) consents to the personal jurisdiction of the state and
federal courts located in the State of Texas in connection with any controversy
related to this Amendment; (ii) waives any argument that venue in any such forum
is not convenient, (iii) agrees that any litigation initiated by the Lender or
the Borrower in connection with this Amendment or the other Loan Documents shall
be venued in either the District Court of Collin County, Texas, or the United
States District Court for the Northern District of Texas; and (iv) agrees that a
final judgment in any such suit, action or proceeding shall be conclusive and
may be enforced in other jurisdictions by suit on the judgment or in any other
manner provided by law. THE PARTIES WAIVE ANY RIGHT TO TRIAL BY JURY IN ANY
ACTION OR PROCEEDING BASED ON OR PERTAINING TO THIS AMENDMENT.

          15.  ENTIRE AGREEMENT. THIS AMENDMENT AND ALL OTHER INSTRUMENTS,
               ----------------
DOCUMENTS AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH THIS
AMENDMENT EMBODY THE FINAL, ENTIRE AGREEMENT AMONG THE PARTIES HERETO AND
SUPERSEDE ANY AND ALL PRIOR COMMITMENTS, AGREEMENTS, REPRESENTATIONS AND
UNDERSTANDINGS, WHETHER WRITTEN OR ORAL, RELATING TO THIS AMENDMENT, AND MAY NOT
BE CONTRADICTED OR VARIED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT
ORAL AGREEMENTS OR DISCUSSIONS OF THE PARTIES HERETO. THERE ARE NO ORAL
AGREEMENTS AMONG THE PARTIES HERETO.

                                      -3-
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          IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed as of the date first written above.

WELLS FARGO BANK MINNESOTA, N.A.                    RF MONOLITHICS, INC.

By: /s/ Brett Marschall                             By: /s/ David M. Kirk
    --------------------------------------------        ------------------------
    Name:  Brett Marschall                              David M. Kirk
           -------------------------------------
    Title: VP & Manager Structured Trade Finance        President
           -------------------------------------

                                      -4-<PAGE>

                                                                   Exhibit 10.55
                                                                   -------------

                                  Amendment 1

RF Monolithics, Inc. (RFM) and Cirtek Electronics Corporation ("Consignee")
agree that the Agreement between RFM and Consignee entitled Manufacturing
Agreement and dated March 23, 2001 (the Agreement) is hereby amended effective
June 1, 2001 as follows:

I.   Paragraph 1. General Definitions.

Add the following definition between the definition for Provided Equipment and
Quarterly Operations Review on page 4:

     Purchased Materials: means Materials that were initially consigned by
Company and were subsequently purchased by Contractor as required in Section 2.1
(e) (ii). Examples of Purchased Materials are package lids and headers.
Materials not included in Purchased Materials are die, adhesives, wire and
marking ink.

II.  Paragraph 2.1 (d)  Approved Vendor List.

Add the following sentence at the end of the paragraph:

     Copies of Company pricing agreements shall be supplied to Contractor for
Purchased Materials. Company will request Approved Vendors to offer Contractor
the same pricing and payment terms as provided to Company for Purchased
Materials.

III. Paragraph 2.1 (e) (v)

Add the following sentence at the end of the paragraph:

     If the assembly yield is below the negotiated yield (parameter Y in
Schedule A) and the Contractor and Company agree, in writing, that the cause for
the lower Assembly Yield is due to poor quality of consigned die, Company will
reimburse Contractor for the unit price of the Purchased Materials plus handling
fee for the number of units constituting the incremental yield loss below the
negotiated yield Y.

IV.  Paragraph 4.1 Price and Payment of Manufacturing Services.

The last sentence, of the first paragraph, is deleted in its entirety and
replaced with the following:

     The invoice amount shall be determined as follows:

     I=(AO-FI)(AP+TP) + (AO+FI)((X+FHC)/Y)

Where:

     "I" is equal to the invoice amount;
     "AO" is equal to the Assembly Outs;
     "FI" is equal to the number of Products (Units) found to be defective at
     the Test Final
     Visual inspection; FI will also include the number of units found to be
     defective at Fine
     and Gross Leak test if the Fine and Gross leak test is part of the test
     flow, typically
     Performed after Electrical Test.
     "AP" is equal to the assembly price; and
     "TP" is equal to the test price.
     "X" is equal to the unit price for Purchased Materials
     "FHC" is equal to a negotiated handling fee (Schedule A)
     "Y" is equal to a negotiated assembly yield factor (Schedule A)
<PAGE>

V.   Schedule A is deleted in its entirety and replaced with the attached
Schedule A, dated June 1, 2001.

IN WITNESS WHEREOF, the parties have caused this Amendment to be executed by
their duly authorized representative this 13 day of June, 2001.

RF MONOLITHICS, INC.                         Cirtek Electronics Corporation

       /s/ David T. Somerville                     /s/ Dennis Chau
--------------------------------------       ----------------------------------
       (Authorized Signature)                      (Authorized Signature)

Name   David T. Somerville                   Name  Dennis Chau
     ---------------------------------           ------------------------------
       (Type or Print)                             (Type or Print)

Title  VP QA & Corporate Development         Title VP Finance
     ---------------------------------           ------------------------------
       (Type or Print)                             (Type or Print)

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